Czechia: SIP providers and connecting a number to the PBX

This page continues the general guide on connecting a provider's number to the PBX: that page covers everything that is the same for any operator — the two trunk modes, what to ask the provider, what to type into the form, network requirements and how to verify the link. Here is the Czech specifics: who sells a number with a SIP trunk in the country, what such an operator hands over and what of it goes into Telephony → "Trunks and connections" → "Add provider".

The data was collected on 9 September 2026 from operator documentation, their tariffs and materials of the regulator ČTÚ; links are in the "Sources" section.

In short#

• You can buy a number with a SIP trunk in Czechia, and the venue needs no permits for it. There is no separate "VoIP licence": electronic communications business runs on a notification to ČTÚ, and the one who notifies is the operator you buy the number from, not you.
• The market is split in two, and that is the main conclusion for the country. The big three — O2, T-Mobile, Vodafone — deliver the SIP trunk over their own IP access line with QoS, not over the internet: T-Mobile says so in plain words in its specification. Our PBX lives in the cloud and its address does not belong to their network, so you have to work with internet VoIP operators.
• Start with Odorik.cz. It is the only operator in the country with a public step-by-step Asterisk guide: server sip.odorik.cz, port 5060, UDP, registration, G.711 A-law codec. The trunk is enabled manually on request, free of charge. Next come FAYN (all parameters published, the login is the number itself) and AXFONE — the FAYN platform that supports both trunk modes.
• The main local trap is seven digits. A Czech national number is exactly 9 digits, of which the first one or two are the telephone area code. The PBX matches a line by the last seven digits, that is, without the area code: Prague's 212 240 258 and the Plzeň region's 312 240 258 are indistinguishable to it.
• The caller number is checked by the network. Since 1 June 2024 an operator must put into the signalling a real subscriber number that can be called back, and since 1 July 2024 incoming calls carrying a Czech caller number are blocked at international interconnection points. In the outbound rule use only the numbers of your own contract.
• Almost everywhere the trunk is enabled by hand. Odorik does it on request, AXFONE asks to be informed in advance that a PBX is being connected, IPEX gives only 4 voice channels by default, and IT Profík's minimum package is 30 simultaneous calls. "Bought it and connected in ten minutes" happens in Czechia only with international providers.
• Paperwork. Czech operators sign the contract with a Czech entity (IČO/DIČ); not one of the checked operators publishes a procedure for a foreign company to buy a number. For a foreign owner it is easier to take a +420 number from an international provider.

Numbers in Czechia#

• The country code is 420. The national number is always 9 digits — that is how the ČTÚ numbering plan puts it. The numbering is closed: the transit zero before the area code is not dialled, the subscriber always dials the full nine-digit number (the rule has applied since 22 September 2002).
• The number is built as an area code (1–2 digits) plus the subscriber part. Area codes from the annex to the numbering plan: 2 — Prague, 31, 32 — Central Bohemia, 35 — Karlovy Vary, 37 — Plzeň, 38, 39 — České Budějovice, 41, 47 — Ústí, 46 — Pardubice, 48 — Liberec, 49 — Hradec Králové, 51, 54 — Brno, 55, 59 — Ostrava, 56 — Jihlava, 57 — Zlín, 58 — Olomouc. Since geographic portability was introduced, the area code is no longer strictly tied to the place.
• Mobile numbers are also 9 digits, in the 60x and 7xx ranges; 800… is toll-free for the caller. We checked these ranges against provider catalogues rather than a separate decision of the regulator.
• Dialling. Inside the country — all nine digits, without +420 and without 00420: FAYN describes it exactly that way on its parameters page. Abroad — 00 plus the country code, or +.
• The emergency call is the single European 112.

On the "Lines" tab the number may be entered in any form: the PBX matches the last seven digits, so both 00420212240258 and 212240258 find the same line.

⚠️ The seven-digit trap. The seven-digit tail is the subscriber part without the area code, so numbers from different regions may collide: 212 240 258 (Prague) and 312 240 258 (the Plzeň area) are identical to the PBX. As long as all of the venue's numbers come from one area, everything is fine; if the operator issues numbers from different regions, compare the tails by hand — "Add a number and routing".

Who sells a number with a SIP trunk#

The five operators below get cards of their own: their trunk mode is known and it is clear what to enter. The incumbents are moved to a separate section — their trunk is designed to run on top of their own access. The rest hand over parameters only after a contract — "under contract".

Odorik.cz#

A Brno VoIP operator with cheap lines and, more importantly for us, with an engineering wiki: it is the only one in the country with a detailed page on connecting a SIP trunk to Asterisk, with examples both for the modern chan_pjsip and for the old chan_sip. A trunk line differs from an ordinary one in that it allows outbound calls under the numbers of your other lines; an ordinary line is turned into a trunk one manually on request — you write to their form and state the maximum number of simultaneous outbound calls. The service is free.

What to enter in the admin panel

What to set up at the provider: create an account and a line → file a request to make the line a trunk one, stating the number of simultaneous outbound calls → ask them to allow a range of numbers for the caller field, otherwise outbound calls will go out under the line's own number → in the incoming call settings point every purchased number at the trunk with a string like sip:<number>@<line number>.

Pitfalls ⚠️ Point incoming calls with the number in the string: in the basic variant sip:@<line number> there is no number in the call at all, and the PBX cannot tell the lines apart — the call is accepted, but a routing rule for a specific number will not fire. Odorik has historically expected the caller number in the Remote-Party-ID or P-Asserted-Identity service headers, which our PBX does not send; since September 2020 the ordinary From field is enough for them, but only on a registered line — check outbound calls with a test call right after connecting. Their examples use a single codec, G.711 A-law, which the PBX has. Source: Odorik SIP TRUNK — připojení za NATem — 09.09.2026.

FAYN Telecommunications#

A Czech operator working since 2001: local numbers, a "virtual mobile", foreign numbers and a cloud PBX of its own. For an external PBX you take an ordinary SIP account on the number — it doubles as the trunk. The parameters are published in full, which makes it the second most transparent operator in the country after Odorik.

What to enter in the admin panel

What to set up at the provider: buy or port a number → take the registration password in self-service → point the number at that account → with several numbers, ask whether they all go to one account (then we tell them apart in "Lines") or each to its own.

Pitfalls ⚠️ The login is a number, not an account name: change the number and the trunk login changes with it. The portal password and the SIP registration password are different things, and using the first one gives "not registered with the provider". The operator's codec list includes G.729, which the PBX does not have, but the same list has G.711 A-law, µ-law and G.722 — they will agree on their own, nothing needs to be switched off. Customers of the former AXFONE platform work on different addresses — see the next card. Source: VoIP — základní údaje pro nastavení zařízení — 09.09.2026.

AXFONE — a platform inside FAYN#

A former standalone operator; its subscribers and platform moved to FAYN, but the platform's technical support is alive and keeps the best Asterisk page in the country — with both trunk modes and ready-made configuration snippets. New customers are put by FAYN on sip.fayn.cz, so ask right away which platform you are being connected to: the AXFONE successors use other addresses (sipcz.fayn.cz, and sipsk.fayn.cz for Slovakia).

What to enter in the admin panel

What to set up at the provider: tell them in advance that a PBX is being connected, not a phone — the trunk is configured on a prior request → choose the mode (dynamic or static) → for the static one give them the PBX public address → agree on the number of voice channels → clarify in which format to send numbers: international with leading zeros (00 plus the number) or national.

Pitfalls ⚠️ For AXFONE the caller number is a mandatory parameter: the operator states plainly that without it the customer is not identified, so in the outbound rule always set "Show as" to your contract number. Their tone dialling is RFC 2833, the same as the PBX uses. Their configuration template includes G.729, but G.711 A-law and µ-law sit next to it, so a common language will be found. The guide is written for the old chan_sip — carry over the meaning of the parameters (address, login, password, mode), not the file lines. Source: Axfone technická podpora — Asterisk — 09.09.2026.

ha-loo / HA-VEL INTERNET#

An Ostrava operator: the mass-market VoIP service ha-loo with credit lines and local numbers, plus its own cloud PBX "ha-loo Centrála". For an external PBX you take an ordinary SIP line: phones, gateways and PBXs register at the operator's central switch over standard SIP, the registration name is your number and the password arrives by e-mail.

What to enter in the admin panel

What to set up at the provider: sign up and top up the credit → buy a local number → point it at the line → ask support about the trunk mode and the number of simultaneous calls per line.

Pitfalls ⚠️ The operator has no public page for the trunk itself — what is published are the parameters of a line, so agree the number of simultaneous conversations and the mode by e-mail. According to their description the client picks the codec and the switch adapts: of the supported ones we share G.711 A-law and µ-law. The operator states channel requirements — zero loss, latency up to 100 ms, jitter up to 10 %; a cloud PBX meets them by itself, but if the operator asks, take the address and ports from "Network and compatibility". Part of the website material is old, so confirm the parameters with support before going live. Source: ha-loo — Jak to funguje — 09.09.2026.

802.cz — the "802 TRUNK" service#

The 802.VOX SIP TRUNK service is meant for exactly our case — "for connecting a customer's VoIP PBX". The website states that 802.cz services are provided by O2 Czech Republic, but unlike O2's own product this trunk is sold by channels and without the operator's own access line. The numbers come from every telephone area of the country, there are nomadic numbers as well, and your own number can be ported (41 Kč a month).

What to enter in the admin panel

What to set up at the provider: pick a tariff by the number of channels → get or port the numbers → request the trunk credentials and the SIP server address → clarify the number format in incoming calls and which numbers are allowed in the caller field.

Pitfalls ⚠️ The server address is not a constant here: it depends on the number and the node, so it may change when a number is ported or a node is moved — check it with the form before connecting and after any change on the operator's side. There is no public technical documentation for the trunk at all, so agree the codecs and number formats by e-mail, using the list from "What to ask the provider". Source: 802.cz — nabízené služby — 09.09.2026.

O2, T-Mobile and Vodafone — a trunk on top of their own access#

There are no "what to enter" tables here on purpose: for all three the trunk is designed as part of their own connection, and for a cloud PBX that is the first question in negotiations, not an implementation detail.

T-Mobile Czech Republic is the only incumbent with published trunk specifications (the R4 and Broadworks platforms), and they explain themselves why it will not fit: "SIP trunk … zřizován prostřednictvím IP přípojky s podporou QoS, nikoli prostřednictvím veřejné internetové sítě" — the trunk is provisioned over their IP access line with QoS, not over the public internet. The customer is given a separate voice address that terminates on the operator's equipment on the premises and serves as the authorisation itself, so no registration is needed. The codecs are compatible (G.711 A-law recommended), tone dialling is RFC 2833, transport is UDP — that is, formally everything matches, but only a PBX sitting behind their access line can connect to this trunk. The specifications have not been reissued since 2016, so verify the border server addresses when connecting.

O2 Czech Republic offers VoIP Connect for connecting an IP PBX, a traditional PBX or VoIP gateways. The codecs are published (G.722, G.729, G.711 A-law) as well as the minute bundles — 300, 1,000, 3,000 and 10,000 minutes from 350, 1,140, 3,210 and 7,850 Kč a month excl. VAT. The service comes together with their data link: the operator promises "postaráme se o vše, včetně datového připojení", a technician visits to check readiness, and the whole process takes 2–4 weeks. The server address and the authorisation mode are not described publicly.

Vodafone Czech Republic publicly promotes a managed and a virtual PBX (Managed PBX, the OneNet platform) rather than a trunk for someone else's PBX; there is no technical trunk specification on the site. It is easy to buy the wrong thing: OneNet and Managed PBX are their own switch, while all we need is the trunk.

What to ask before signing: is it possible to deliver the trunk over the ordinary internet to an external PBX with a public static address, without their equipment on the premises; which server address will be publicly routable; which authorisation mode. If the answer "a public address" does not come, take a number from an operator in the cards above — porting takes two working days.

Providers "under contract"#

These operators do have a trunk for someone else's PBX and sell it as a standard service, but the server address, login and password are issued only after a contract — so there can be no "what to enter" table here. Ask for the parameters using the list from "What to ask the provider". Spell out the main point separately: the PBX is in the cloud, not on the venue's premises — it is worth getting that confirmed in writing before paying.

• Quantcom — a Prague operator with its own fibre network, the only one among the checked large operators that explicitly promises "connection over the ordinary internet, regardless of the access provider". Numbers: local, 800, 900 and international. ⚠️ It can do SIP over TLS with media encryption and may offer that as "more secure" — ask for plain UDP or TCP without encryption, the PBX does not support encrypted trunks.
• Fastcom — a Prague operator with a "SIP trunk" product for direct connection of IP PBXs of companies, operators and institutions; its description also mentions secure TLS connections. It publishes no parameters. ⚠️ Its product showcase looks very much like Quantcom's — check which of them you actually signed with, so as not to mix up the parameters.
• IPEX — a České Budějovice operator known for its contact centre and virtual PBX; its SIP trunk serves "for connecting telephone exchanges and call centres", including ones owned by the customer. The service includes access to emergency numbers with caller localisation — the only operator in our list that promises this outright. ⚠️ By default you get 4 voice channels: a venue will hit that ceiling silently at peak time and callers will get a busy tone, so raise the channel count at once.
• VoIPSUN — a Prague company that is both an operator and a PBX vendor; its trunk "will connect your or any other SIP exchange to the telephone network" and, per the service description, without a cap on simultaneous calls. Tariffs: Basic 0 Kč a month (activation 300 Kč), Comfort 80 Kč, Business 120 Kč, all excl. VAT; number porting is free and takes two working days. ⚠️ It does not publish its network parameters; the documentation of its own PBX shows the platform can do both registration and a static address — ask on activation which mode you will get.
• IT Profík — a small operator-reseller, useful as a sample of the most common model in the country: after the trunk is activated you get an access name, a password and a server address. The monthly fee is 0 Kč, connection is 0 Kč, availability 99.9 %, and there is a portal with call records. ⚠️ The minimum package is 30 simultaneous calls, noticeably more than a single venue needs; the number format in incoming calls is clarified by e-mail.

International providers with Czech numbers#

Czech numbers are sold by DIDWW, Telnyx, Twilio and Zadarma; for a foreign owner this is often the only route, because local operators sign contracts with a Czech entity.

• DIDWW — since 18 November 2024 it sells its own local +420 numbers: activation is instant from the portal or through the API, and Czech numbers can also be ported. The country requirements are published on a separate page.
• Telnyx — Czech numbers from $1 a month, porting available. The country requirement: an address proof no older than three months, and the end user must be physically located in the country of the number; for EU customers a passport or an ID card of any member state is enough.
• Twilio — three types of numbers: local and mobile (+420 73…), plus toll-free and national ones (+420 800…, +420 910…). A local number needs an address within the prefix area (a PO box will not do) and a document — a bill, a lease, a tax notice or a company register extract; for mobile and toll-free numbers the address may be anywhere.
• Zadarma — Prague numbers +420 2: you cannot pick a particular number, a random one is issued, connection is free, the monthly fee is around $2, and there are three or more inbound channels. Documents: a copy of an ID document from both sides and an address in the region of the city where the number is ordered. The number can be pointed at an external PBX as well.

The parameters and modes of these providers are already described in the catalogue when adding a provider — the server address and the mode fill in by themselves, there is no need to copy them from the country page.

For a cloud PBX an international provider is a workable fallback: it offers registration or IP authorisation without being tied to a Czech access line. The one drawback is the document check with a local address for geographic numbers.

Number porting#

• Portability of the nine-digit number is fixed by the numbering plan and the sector law: the operator is obliged to provide it.
• Since 1 April 2020 the OKU code (ověřovací kód účastníka) has been in use: the subscriber takes the code from the current operator and hands it to the new one. The standard porting time is two working days, the service interruption is no longer than one working day, and the receiving operator notifies the donor within one working day.
• Operator practice confirms this: VoIPSUN ports numbers free of charge in two working days with an interruption of no more than a working day, and at 802.cz a ported number costs the same as an ordinary one.
• ⚠️ On the porting day the number may stay silent for a few hours — plan it for off-peak time and keep the old channel or a temporary forwarding until the port is confirmed.
• The number is ported to whoever signed the contract. A number held by an individual is ported the same way, but a trunk contract usually requires an IČO — check whose name the number is in before ordering the trunk.

Rules and paperwork#

If it does not work#

1. The operator talks about "our own access line" or issues an address from their network. That is the T-Mobile and O2 scheme: the trunk is delivered over their QoS link, and the address they issue serves as the authorisation. From the cloud it is unreachable — demand a publicly routable server address or take a number from an operator in the cards above.
2. Odorik: calls arrive but the line is not identified. Incoming calls are pointed at the trunk by a string without a number. Change the route in the portal to the variant with the number — sip:<number>@<line number>.
3. Odorik: outbound calls go out with the wrong number or are rejected. The operator checks the caller number against the range allowed for the line, and the range is opened on request. Until the request goes through, leave "Show as" empty — the line's own number will be used.
4. FAYN: "not registered with the provider". Two typical causes: the account name was entered as the login instead of the nine-digit number, or the portal password was used instead of the SIP registration password from the "Nastavení služeb" section.
5. The call connects but there is silence. Only G.729 is left on the account — it appears in the templates of AXFONE, ha-loo, FAYN, T-Mobile and O2, and the PBX does not have it. Ask them to enable G.711 A-law: every Czech operator on this list has it.
6. The operator offers an encrypted trunk only. TLS and media encryption are supported by Quantcom and Fastcom. Ask for plain UDP or TCP — the PBX does not support encrypted trunks.
7. The server address stopped responding. At 802.cz it is issued by a form for your number and changes when a number is ported or a node moves; at FAYN the address depends on the platform (sip.fayn.cz, sp.fayn.cz or the AXFONE successor addresses). Check the address with the operator and re-run "Check the link".
8. Two numbers land on one line. Numbers from different areas share the same last seven digits. Separate such lines by hand.
9. Some callers get a busy tone. The channels ran out: IPEX gives four by default, 802.cz gives as many as the tariff includes. Raise the channel count with the operator.

Causes that do not depend on the country are in "If calls do not go through"; the SIP trace in the trunk menu is described there as well.

Frequently asked questions#

Whom should I take a number from if nothing is connected yet?#

Odorik.cz: it is the only Czech operator with a public Asterisk guide, it has clear parameters (sip.odorik.cz, UDP/5060, registration), cheap lines and free trunk activation on request. Alternatives of the same class are FAYN (all parameters published, the login equals the number) and AXFONE if you need a trunk with IP authorisation.

I already have a number with O2 or T-Mobile. Will it work with a cloud PBX?#

The number itself will, if the operator agrees to deliver the trunk over the ordinary internet to the PBX public static address. The standard scheme for both is different: the trunk runs over their QoS IP access line and terminates on their equipment on the venue's premises, and with T-Mobile the address they issue doubles as the authorisation. Ask about this before signing; if the answer "a public address" does not come, it is easier to port the number to an operator from the cards above — porting takes two working days.

Do I need a Czech company to get a number?#

For a local operator, yes: the contract is signed with a Czech entity by IČO. None of the checked operators publishes a procedure for a foreign company, so a foreign owner will find it easier to take a +420 number from an international provider. Mind that Telnyx needs a fresh address proof and presence in the country, and Twilio needs an address within the prefix area for a local number.

How many channels should I order?#

A channel is one simultaneous conversation; a venue usually needs 2–4. Market reference points: 802.cz sells packages of 5, 10, 20 and 30 channels (248–694 Kč a month excl. VAT), IPEX gives 4 by default, IT Profík's minimum is 30, and VoIPSUN states no cap on the number of calls in its service description. With Odorik you state the number of simultaneous outbound calls yourself in the trunk request.

Can I show a different number on outbound calls?#

In practice, no. Since June 2024 an operator must pass a real subscriber number reachable for a call back, and since July 2024 calls from abroad carrying a Czech number are cut at international interconnection points. On top of that Odorik checks the number against the line's allowed range, and T-Mobile silently replaces a number outside the allocated range with its own system one. Put only your contract numbers into "Show as".

Will calls to 112 work through the trunk?#

For a local operator this is a legal obligation, but access to emergency numbers with caller localisation is promised outright in the service description only by IPEX — with the others get it confirmed in writing. On our side, remember that numbers shorter than four digits are not picked up by the general outbound rule, so 112 needs a rule of its own. With international providers an emergency call is not always available.

Sources#

All links checked on 09.09.2026.

Operators

• Odorik.cz — Odorik SIP TRUNK, připojení za NATem (Asterisk configuration): https://www.odorik.cz/w/freepbx:siptrunk
• FAYN — VoIP: základní údaje pro nastavení zařízení: https://www.fayn.cz/pece-a-podpora/navody-a-nastaveni/voip-parametry
• FAYN — support portal, basic device parameters: https://podpora.fayn.cz/803364-Z%C3%A1kladn%C3%AD-info-k-nastaven%C3%AD-za%C5%99%C3%ADzen%C3%AD
• AXFONE — technická podpora, Asterisk: https://podpora.axfone.cz/cz/547-ustredny/368-asterisk
• ha-loo / HA-VEL — Jak to funguje: https://ha-loo.ha-vel.eu/cz/informace.php?top=2
• 802.cz — nabízené služby, telefon (802 TRUNK and tariffs): https://www.802.cz/sluzby-telefon/
• 802.cz — Zjištění SIP serveru: https://www.802.cz/zjisteni-sip-serveru/
• VoIPSUN — hlasové služby, SIP trunk: https://www.voipsun.cz/hlasove-sluzby/
• Quantcom — Trunk: https://www.quantcom.cz/firma/hlas/trunk/
• Fastcom — SIP trunk: https://fastcom.cz/operator/hlas/sip-trunk/
• IPEX — ceník Kontaktní centrum a další služby: https://www.ipex.cz/wp-content/uploads/2024/01/Cenik-Kontaktni-centrum-IPEX-1.6.2023.pdf
• IT Profík — připojení VoIP ústředny: https://www.itprofik.cz/produkty-a-sluzby/hlasove-sluzby-voip/iax2-sip-trunk/
• T-Mobile CZ — technická specifikace hlasového propojení SIP trunk R4: https://www.t-mobile.cz/dcpublic/Sluzba-Popis_hlasoveho_propojeni_SIP_R4.pdf
• O2 — VoIP Connect: https://www.o2.cz/podnikatele-a-firmy/volani/voip-connect
• Vodafone CZ — pobočkové ústředny (Managed PBX): https://www.vodafone.cz/verejna-sprava/volani/managed-pbx/
• DIDWW — its own local DID numbers in the Czech Republic: https://news.didww.com/2024/11/18/didww-adds-its-own-local-did-numbers-in-the-czech-republic-420/
• Telnyx — Czech Republic DID requirements: https://support.telnyx.com/en/articles/5464141-czech-republic-did-requirements
• Twilio — regulatory guidelines for the Czech Republic: https://www.twilio.com/en-us/guidelines/cz/regulatory
• Zadarma — Prague +420 2 numbers: https://zadarma.com/en/tariffs/numbers/czech-republic/prague/

Regulator and numbering

• ČTÚ — Číslovací plán veřejných telefonních sítí: https://ctu.gov.cz/1/download/cislovaci-plan-verejnych-telefonnich-siti_1114435245.pdf
• ČTÚ — the first measures against spoofing from 1 June 2024: https://ctu.gov.cz/tz-od-1.-cervna-budou-platna-prvni-opatreni-proti-spoofingu
• ČTÚ — the measures against spoofing work, millions of calls blocked: https://ctu.gov.cz/opatreni-uradu-proti-spoofingu-funguji-blokovany-jsou-miliony-hovoru-mesicne-pocet-podvodu-klesa
• ČTÚ — information for subscribers on number porting: https://ctu.gov.cz/informace-pro-ucastniky-o-sluzbe-preneseni-telefonniho-cisla

Related pages#

• Connecting a provider's number to the PBX — the general steps, trunk modes, network, link check.
• Setting up SIP phones — how to connect desk phones and DECT to extensions.