Slovakia: 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, the network requirements and how to verify the link. Here is the Slovak 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 and materials of the regulator; links are in the "Sources" section.

In short#

• You can buy a number with a SIP trunk in Slovakia, and the venue needs no permits for it. There is no separate "VoIP licence": under the act 452/2021 Z. z. o elektronických komunikáciách the business runs on a notification to the regulator, and the one who notifies is the operator you buy the number and the trunk from, not you.
• Start with Slovak Telekom. This is a rare case for Europe: the technical conditions for connecting a third-party SIP PBX to the Business Trunk service are published in full — server sip.vvn.telekom.sk, UDP, port 5060, codecs G.711 A-law, G.711 µ-law and G.722 (the same set our PBX has), DTMF over RFC 2833.
• For a small venue VIPTel is simpler. It is the only operator in the country with an official guide written for Asterisk: sip.viptel.sk, registration, login and password from the self-care portal, numbers and porting ordered there too.
• The main local trap is the "call on the pilot number". In the registration mode Slovak Telekom puts the number of the trunk's pilot account into the inbound call, while the number actually dialled travels in another header. The PBX matches lines by the former, so every number of such a trunk looks the same: keep one line on a Telekom trunk until the operator confirms a different format.
• The second trap is G.729 first in the list. Slovanet's recommended codec order starts with G.729, and SWAN's list has no G.722 at all. The PBX only speaks G.711 A-law, G.711 µ-law and G.722 — ask the operator to put G.711 A-law first, otherwise the call connects with no audio.
• The third one is seven digits. A Slovak national number is exactly 9 digits. The PBX matches a line by the last seven, so Bratislava numbers are not compared in full, and two regional numbers from different areas may share the same tail.
• UDP only, and no encryption. Slovak Telekom states plainly that the transport must be UDP; VIPTel's encrypted variant on port 5061 is not available to our PBX — encrypted trunks are not supported.
• Paperwork. Local operators sign a contract with a Slovak entity (IČO/DIČ); none of the operators we checked publishes a procedure for a foreign company to buy a number. A foreign owner will find it easier to take a +421 number from an international provider.

Numbers in Slovakia#

• Country code — 421, international prefix — 00 or +, national prefix — 0 (not part of the number itself).
• A national number is exactly 9 digits, as written in the national numbering plan (vyhláška č. 286/2022 Z. z.). This applies to direct-dial (DDI) numbers in a trunk as well.
• Geographic areas — 25 regions. Bratislava has code 2 and an eight-digit subscriber number; all the others have a two-digit code and seven digits: 31 Dunajská Streda, 32 Trenčín, 33 Trnava, 34 Senica, 35 Nové Zámky, 36 Levice, 37 Nitra, 38 Topoľčany, 41 Žilina, 42 Považská Bystrica, 43 Martin, 44 Liptovský Mikuláš, 45 Zvolen, 46 Prievidza, 47 Lučenec, 48 Banská Bystrica, 51 Prešov, 52 Poprad, 53 Spišská Nová Ves, 54 Bardejov, 55 Košice, 56 Michalovce, 57 Humenné, 58 Rožňava.
• Mobile numbers — a three-digit code and six digits (or a four-digit code and five), the same nine in total.
• Toll-free and "blue" numbers — 0800 xxx xxx (zelené linky) and 0850 xxx xxx (modré linky, shared cost); operators sell them as a separate product.
• Dialling. Inside your own area the subscriber number without 0 and without the area code is allowed, between areas and to mobiles — 0 and nine digits, abroad — 00 or + and the number. The emergency call is the single European 112, free of charge by law.

In the "Lines" tab the number can be entered in any form: the PBX matches the last seven digits, so both 00421255667788 and 0255667788 find the same line.

⚠️ The seven-digit trap. For a Bratislava number (code 2 plus eight digits) only seven of the eight digits are compared — the first digit of the subscriber part is lost, and two similar numbers merge into one line. For regional numbers (code plus seven digits) the tail equals the whole subscriber part, so 041 5123456 (Žilina) and 051 5123456 (Prešov) look identical to the PBX. If the venue has several numbers, compare their tails by hand — "Add a number and routing".

Who sells a number with a SIP trunk#

The four operators below have their own cards: their server address and trunk mode are known, so it is clear what to enter. The rest hand over the parameters only after a contract — "under contract".

Slovak Telekom — Magenta Office BiznisTRUNK#

The largest operator in the country. The service for a third-party PBX is sold as BiznisTRUNK (the "Magenta Office" range) and called Business Trunk in the technical documents, and this is the only Slovak operator that published the connection conditions in full: two PDFs of version 8.2 with addresses, codecs and message examples. There are two modes — with a registered pilot account (for a PBX with a single SIP interface) and with static routing without registration; the first one suits us.

What to enter in the admin panel

What to set up with the provider: order Magenta Office BiznisTRUNK from a business manager → choose the mode with a registered pilot account → get the hand-over protocol with the pilot account number and the password → ask for all the direct-dial numbers you need to be put into one trunk group → give the engineer the static address of the PBX from the "Server" tab and confirm that the connection runs over the public internet, not through the operator's own network.

Pitfalls ⚠️ According to the operator's documents as of 9 September 2026, for connections from the public internet it names a separate outbound proxy address 195.146.137.186 — when ordering, check with the engineer which name or address the signalling should go to: the form has a single field. Only the pilot account registers, no matter how many numbers the trunk holds: if that registration drops, every number goes down at once. In the registration mode the inbound call carries the pilot account number, so a "which line was called" rule will not tell the numbers apart on such a trunk — keep one line on it. Authorisation of outbound calls is mandatory in both modes and cannot be turned off; that is exactly why the mode without registration does not fit — in it the PBX sends no login and password, and the calls are rejected. The operator expects the employee's number in the P-Preferred-Identity header, which the PBX does not send by default: without a request to support every call leaves under the pilot account number, and the caller ID field will not work. Source: ST BT setting v8.2 — pilot, EN — 9 September 2026.

VIPTel (VM Telecom)#

A Slovak VoIP operator, "hlas pre Váš biznis": fixed lines, a cloud PBX, special numbers, number porting. It is the only one in the country with an official guide written for Asterisk — separate pages on setting up a VIPTel trunk and a VIPTel account. The self-care portal is self-service, so the credentials are visible as soon as the service is active.

What to enter in the admin panel

What to set up with the provider: order the business plan → create a trunk in the portal (one per site if there are several) → attach the numbers you bought to it → port the venue's existing number if needed → if there are several numbers, ask in which form the dialled number arrives.

Pitfalls ⚠️ The operator offers an encrypted variant on port 5061 — it does not suit our PBX, take the plain one. Codecs are not named in the guide: ask support whether G.711 A-law is enabled on the trunk. The guide is written in Asterisk configuration terms; the mapping is simple: server address → "SIP host", access name → "Login", password → "Password". The operator suggests putting a geographic number into each extension's caller ID field — with us that is the caller ID setting in the outbound rules. The parameters above were taken from a snapshot of the operator's page dated 11 November 2025 — verify them on the live site before you connect. Source: viptel.sk/asterisk — 9 September 2026.

SWAN — IP Trunk and IP Telefónna linka#

The second largest operator on the corporate market, with its own infrastructure (its mass-market mobile brand is 4ka). Its voice range includes IP Trunk as a separate product: "you have your own PBX and need to connect it to the public telephone network" — a variable number of voice channels, number porting, an SLA and compatibility with legacy exchanges through converters. The product page gives no technical parameters; what is published are the parameters of the neighbouring service, IP Telefónna linka.

What to enter in the admin panel

What to set up with the provider: request a quote for IP Trunk → state in the request that the PBX lives in the cloud with a static address and the connection is needed over the public internet, not through the operator's access line → agree the number of voice channels → ask for G.711 A-law to be enabled → agree the porting of your numbers.

Pitfalls ⚠️ The published codec list of the service contains G.711 A-law, G.711 µ-law, G.729 and GSM, but no G.722 — ask for A-law explicitly, otherwise the operator may leave G.729 alone and there will be no audio. The platform expects a re-registration interval of at least 900 seconds: our PBX re-registers more often, which is allowed, but ask support whether the platform throttles frequent registrations. DTMF is RFC 2833, which the PBX supports. Source: Popis služby IP Hlas — nastavenia (PDF) — 9 September 2026.

Slovanet#

A national alternative operator: internet, TV, voice and corporate networks. Voice is a VoIP service over any access line, and the official sheet "Základné nastavenia pre VoIP" gives the parameters in full. There is no product called "SIP trunk" on the site: what is sold is a SIP account per number, and it works as the link to the PBX.

What to enter in the admin panel

What to set up with the provider: order the VoIP service under the VoIP tariff (a geographic or a non-geographic number) → ask for G.711 A-law to be put first → find out how many simultaneous calls one account allows and how many numbers can be routed to it → ask in which form the dialled number arrives.

Pitfalls ⚠️ The codec order recommended by the operator starts with G.729, which the PBX does not have: if only that one is left on the account, the call connects but there is no audio. Slovanet leaves the outbound proxy field empty — our form has no such field at all, and that is fine. If registration fails, ask support about the REALM and DOMAIN parameters: the operator asks to fill them with the same server name only in the cases where registration does not go through without them. The document describes a line, not a trunk with a group of numbers, so agree the number of numbers per account in writing. Source: Základné nastavenia pre VoIP (PDF) — 9 September 2026.

Providers "under contract"#

These operators either have a service for a third-party PBX or, on the contrary, have not confirmed one publicly, but the server address, login and password are handed over only after a contract — so there can be no "what to enter" table here. Ask for the parameters using the list in "What to ask the provider" and always spell out the main thing: the PBX lives in the cloud, not on the venue's premises, and it needs a trunk over the ordinary internet to a public static address.

• O2 Business Services — Voice Connect. The product is described as a "cost-optimised replacement for connecting the customer's telephone exchange": your PBX is connected through O2's infrastructure, usually over their own access line, with a full range of voice gateways and voice traffic prioritisation. ⚠️ There is a high chance the service is sold only together with O2 access — in which case it does not connect to a cloud PBX at all; ask before you sign. The operator also has its own cloud PBX and 0800/0850 numbers — do not mistake those for a trunk.
• Orange Slovensko. The largest mobile operator, with a fixed-line range as well. For corporate telephony the site publicly names PBX rental and maintenance, a voice private network and corporate communications management; there is no separate "SIP trunk to your PBX" product, and the price of a solution is set individually. ⚠️ Ask them directly: a trunk to our exchange in the cloud, over the public internet, with a static address — and check whether their managed PBX is required as part of it.
• Optimal Call by Netfon. A Žilina VoIP provider that addresses owners of their own PBX head-on: "if you already own a branch exchange, moving to a SIP Trunk should be simple", and you run the exchange yourself. It sells Slovak numbers, ports existing ones and offers 0800/0850 and foreign numbers. ⚠️ It publishes neither a server address nor an authorisation mode; its own rule of thumb for capacity is one trunk per three phones, more for a contact centre.
• KOMPaaS Slovensko. The Slovak arm of an international platform: virtual numbers, a cloud PBX, CRM integrations. The SIP trunk is a separate product with its own numbering plan, channels are added one at a time, the price is €2.99 per voice channel per month. Sign-up is self-service, so the parameters are visible in the portal even before a contract. ⚠️ This is not a holder of Slovak numbering but a reseller: check whose numbering is named in the contract and what happens to the number if you leave.
• ANTIK Telecom. A regional operator from Košice; voice is sold as a public telephone service connected through their gateway or IP phone, with requirements for phones you buy yourself. There is no "trunk for a third-party PBX" product on the site. ⚠️ With regional operators telephony is almost always tied to their own internet access — ask whether they hand a SIP account "outwards".
• VNET. A Bratislava operator for businesses and homes. A VoIP line is described publicly, but there is no separate trunk on the site. ⚠️ The product is positioned as a home line — a venue will need a corporate contract; ask for an account for an external PBX and a static address.

International providers with Slovak numbers#

Slovak numbers are sold by DIDWW, Telnyx and other international services; for a foreign owner this is often the only route, because local operators sign contracts with a Slovak entity.

• DIDWW — local +421 numbers are sold by city (for example +421-46 Prievidza), and +421-800 toll-free numbers exist too. Provisioning happens from the portal; the modes are a static endpoint or dynamic registration.
• Telnyx — both local and toll-free Slovak numbers are available. A local number requires a copy of the representative's passport, the company name and its registration certificate, a contact phone number, an address inside the same area code as the number, and proof of address no older than three months. A toll-free number requires a registration document, a VAT number, an address anywhere in the world and mandatory business use.
• Twilio, Vonage, Plivo, Bandwidth, Sinch, Infobip, Zadarma, Sonetel — Slovakia is inside the European coverage of most of them, but check that a specific +421 is in stock by searching in the provider's portal: none of them publishes a dedicated page for the country.

The parameters and modes of these providers are already described in the catalogue when you add a provider — the server address and the mode are filled in for you, there is no need to copy them from a country page. What is common to all international providers: the caller ID may only be your own number, access to emergency numbers is a separate service or is missing altogether, and a local address is required exactly where the regulator requires it.

Number porting#

• Number portability is fixed by the act and by a separate decree on the details of portability (vyhláška č. 431/2022 Z. z.); check the exact deadlines and the form of the application with the receiving operator.
• Taking the venue's existing landline number to a VoIP operator is routine in practice: porting is offered as a service by SWAN, VIPTel and Optimal Call.
• Porting is initiated by the receiving operator. The number must belong to the same entity that signs the new contract: a number held by an individual has to be transferred to the company first.
• ⚠️ On the day of the port the number may stay silent for a few hours — schedule it outside peak time and keep a temporary forwarding in place until it is confirmed.
• After the port the emergency-call address is re-registered with the new operator. Even when the number rings in a cloud PBX, the operator's records keep the address you gave in the contract — put the venue's real address there.

Rules and paperwork#

If it does not work#

1. Slovak Telekom: calls arrive, but it is always the same line. That is the normal behaviour of the registration mode — the inbound call carries the trunk's pilot account number. Keep one line on this link and build the per-number handling on the operator's side, or ask them about a mode in which the dialled number is passed on.
2. Slovak Telekom: outbound calls show the wrong number. The operator expects the employee's number in the P-Preferred-Identity header, which the PBX does not send by default, so the calling field carries the pilot account number. Write to our support — sending the number in that header is enabled on the server side.
3. Slovak Telekom: you chose the mode without registration and outbound calls are rejected. In that mode the operator still requires a login and a password on outbound calls, while the trunk form shows those fields only when registration is on. Switch to the mode with a registered pilot account.
4. The call connects but there is silence one way or both. Only G.729 is left on the account: it comes first in Slovanet's recommendations and appears in SWAN's list. Ask the operator to enable G.711 A-law — every Slovak operator in this list supports it.
5. "Not registered with the provider" on Slovak Telekom. The login is the pilot account number without the leading zero — with the zero the registration fails. Also check that you have not confused the hand-over protocol with the credentials of the operator's own cloud PBX.
6. The operator only offers an encrypted connection. VIPTel has such a variant on port 5061. Ask for plain UDP — the PBX does not support encrypted trunks.
7. The operator says the service only runs over its own access line. That is how O2's Voice Connect and the regional operators' lines are built. Such a trunk is unreachable from the cloud — insist on a publicly routable server address, or take a number from one of the operators in the cards above.

The common causes — a wrong login, a disabled line, closed ports — are covered in "If calls do not go through".

Frequently asked questions#

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

With local operators, essentially yes: the contract is signed with a Slovak entity holding an IČO and a DIČ. If you have no company in Slovakia, take a +421 number from an international provider, but prepare the registration documents and proof of an address inside the number's area code.

Which operator should I choose if I want as little correspondence as possible?#

VIPTel: the portal is self-service, the trunk and the numbers are created there, and the operator publishes the connection parameters itself. Slovak Telekom has the best documentation, but that means a contract through a business manager and a hand-over protocol.

Can several numbers live on one Slovak Telekom trunk?#

A trunk group can hold any number of them, and the operator asks for all of them to be put into one group. In the registration mode, however, the PBX cannot tell which of them was called: routing per number needs either a separate link per number or handling on the operator's side.

Why can I not take an encrypted trunk — is it not safer?#

The PBX accepts SIP over UDP and TCP without encryption; encrypted trunks are not supported. The traffic runs between the operator's network and the cloud, so an ordinary trunk has no "through the venue's network" leg where it could be intercepted.

Will an ordinary residential VoIP line do instead of a trunk?#

Often yes: with Slovanet and SWAN an external PBX uses exactly a SIP account per number. Ask the operator two things — how many simultaneous calls one account allows and whether several numbers can be routed to it.

Sources#

Operators

• Slovak Telekom — Business Trunk, connection with a registered pilot account (PDF, v8.2): https://media.acp.cdn.telekom.sk/x/8c64541354/st_bt_setting_v8-2_pilot_en.pdf
• Slovak Telekom — Business Trunk, static routing (PDF, v8.2): https://media.acp.cdn.telekom.sk/x/b0529c285d/st_bt_setting_v8-2_static_en.pdf
• Slovak Telekom — Magenta Office: https://www.telekom.sk/biznis/magenta-office
• SWAN — IP Trunk: https://www.swan.sk/firmy/hlasove-sluzby/ip-trunk/
• SWAN — Popis služby IP Hlas, nastavenia (PDF): https://www.swan.sk/subory/1553/dokumenty/navody-a-nastavenia/IP%20Hlas-nastavenia.pdf
• VIPTel — setting up a trunk on Asterisk: https://www.viptel.sk/asterisk
• Slovanet — Základné nastavenia pre VoIP (PDF): https://www.slovanet.net/wp-content/uploads/2023/06/slovanet_telefonovanie-voip_zakladne-nastavenia.pdf
• Slovanet — the VoIP tariff (PDF): https://www.slovanet.net/wp-content/uploads/2023/06/cennik_voip_10_2024_v1.pdf
• O2 Business Services — Voice Connect: https://business.o2.sk/voice-connect
• Orange Slovensko — voice communications for business: https://www.orange.sk/biznis/prepojenie-pobociek/hlasova-komunikacia
• Optimal Call — SIP Trunking and trunk FAQ: https://optimalcall.com/sip-trunk-faq/
• KOMPaaS Slovensko — SIP Trunking: https://kompaas.sk/produkty/sip-trunk/
• ANTIK Telecom — telephony: https://www.antik.sk/telefonovanie
• VNET — the VoIP fixed line: https://www.vnet.sk/sk/na-doma/hlas/

Regulator and numbering

• Zákon č. 452/2021 Z. z. o elektronických komunikáciách: https://www.slov-lex.sk/static/SK/ZZ/2021/452/20220201.print.html
• Vyhláška č. 286/2022 Z. z. o národnom číslovacom pláne: https://static.slov-lex.sk/static/SK/ZZ/2022/286/20220819.print.html
• The register of electronic communications undertakings: https://www.teleoff.gov.sk/urad/odbory-oddelenia/odbor-regulacie-elektronickych-komunikacii/zoznam-podnikov/

International providers

• Telnyx — Slovakia DID requirements: https://support.telnyx.com/en/articles/5467032-slovakia-did-requirements
• DIDWW — Slovakia +421 local phone numbers: https://www.didww.com/phone-numbers/local-numbers/Slovakia/Local

Related pages#

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