United Kingdom: SIP providers and connecting a number to the PBX

We do not issue numbers: the venue buys a UK number from a carrier or a telephony service and brings it into its own PBX as a trunk. The common steps — trunk modes, form fields, network and testing — are covered in the overview "Connecting a provider number to the PBX"; this page covers only what is specific to the United Kingdom: where to get the number, what the provider issues and what of it goes into the admin panel.

The data on this page was collected on 9 September 2026 from provider documentation and Ofcom materials; the links are in "Sources".

In brief#

• The United Kingdom is the most self-service trunk market on our country list. The venue buys a number with a SIP trunk itself, on a monthly contract, with no account manager: five carriers publish the server address and the parameters openly, and four of them have written a guide for Asterisk specifically. The venue needs no licence — the obligations of a communications provider are carried by whoever sells you the trunk.
• The first candidate is sipgate trunking. Both the server address (sipconnect.sipgate.co.uk) and the prices and codecs are public; the mode is registration; the incoming call carries the full number in international format, so lines are distinguished normally. Next come Andrews & Arnold (no limit on simultaneous calls, both modes work) and Voipfone (a landline number for £3 per month).
• The main local pitfall: half of the carriers send the trunk login instead of the number. Voipfone, Yay.com, Orbtalk and Andrews & Arnold all do this: the call is accepted, but the PBX cannot pick a line by number. With a single number this goes unnoticed; if there are several numbers and each needs its own scenario, take a provider that sends the number: sipgate, VoiceHost, Voiceflex, Simwood.
• The second one is London 020 numbers. A line is identified by the last seven digits, while 020 numbers have an eight-digit subscriber part: 020 7946 0958 and 020 8946 0958 are the same for the PBX. For two venues in London this is a real scenario, so check the endings when ordering a second number.
• 999 and 112 cannot be dialled through the PBX: these are three digits, while outbound rules work from four. Keep a mobile phone on shift — if the internet goes down, the PBX will not place an emergency call anyway. Give the provider the correct postal address of the venue: that is exactly what goes to the emergency services.
• The paperwork is about an address, not a passport. Local carriers ask for a confirmed UK address (sipgate posts a letter with a code to it and does not switch telephony on until the code is entered). A foreign company without a UK address will find it easier to take a number from an international provider — see the relevant section below.

Numbers in the country#

The country code is +44. Inside the country the number is dialled with a leading zero (020 7946 0958), an international call starts with 00 and the country code. In international format the leading zero is dropped: 020 7946 0958 → +442079460958 — and that is how the number is entered in "Lines".

• Length. Most geographic numbers have a 10-digit national number: 020 plus 8, 0113 plus 7, 01234 plus 6; some older five-digit area codes have 9 digits. Mobile numbers 07xxx xxxxxx are 10 digits.
• Ranges: 01 and 02 are geographic; 03 is "UK-wide" at the geographic rate (030 is only for charities and public bodies); 056 are internet telephony numbers not tied to a geographic area; 07 is mobile; 080 is freephone; 084 and 087 are service numbers at a higher rate; 09 is premium rate.
• Service numbers: 999 and 112 are the emergency numbers, 101 is the police for non-emergencies, 111 is the NHS medical line. All of them are shorter than four digits.
• What form the number arrives in on an incoming call — there is no single rule in the country, and this is the main nuance:

⚠️ What this means for several numbers. If the provider sends the login, all the numbers will arrive in a single scenario. Ask whether number delivery can be enabled (Yay.com has an incoming trunk name setting for this, Andrews & Arnold has number blocks with a base group number). If it cannot, then either one number per trunk, or a second trunk with another carrier.

Who issues a number with a SIP trunk#

The first eight rows are providers whose parameters are published or issued on connection; each of them has a "What to enter in the admin panel" table below. The rest mean correspondence with an account manager or somebody else's reseller account.

sipgate trunking#

The British arm of the German sipgate: a separate product built for exactly our task — "connect your own PBX to the telephone network". It is the only carrier in the country that publishes everything at once: the server address, the port, the codecs, the firewall networks and the prices. The contract is monthly, with no setup fee.

What to enter in the admin panel (Telephony → "Trunks and connections" → "Add provider" → the "SIP trunk (custom provider)" card):

What to set up at the provider: register online → enter the code from the paper letter (it arrives within 2–3 working days, and until then telephony does not work) → choose a plan by the number of simultaneous incoming calls → assign the purchased number to the trunk → check that the trunk goes "online" after our registration.

Plans and codecs. Starter £4.95 gives one incoming channel, Regular £8.95 two, Plus £19.95 five, and above that come enterprise plans for 10/25/50 channels. The platform codecs are G.711 in both variants, G.722 and GSM, so compatibility with the PBX is complete; they do not offer trunk encryption (TLS/SRTP) at all, and we do not need it.

Pitfalls ⚠️ The Starter plan gives one incoming channel: a second simultaneous call to the restaurant will not get through, so the minimum for a venue is Regular. The "Present as" field will not work on this trunk: sipgate takes the presentation number from a separate SIP header that our PBX does not send by default, so the trunk number will be shown instead. If you need to choose the number for outgoing calls, write to our support. Presenting somebody else's number is impossible in principle: only numbers from your sipgate account are allowed.

Source: How do I configure Asterisk for sipgate trunking?, Service Specification — 09.09.2026.

Andrews & Arnold (AAISP)#

A small engineering-minded provider with the best technical documentation in the country. It has no separate "trunk" product: any VoIP account acts as a trunk, and there is no limit on the number of simultaneous calls either — a rarity on the British market.

What to set up at the provider: buy or port a number → set its SIP password in the control pages → for incoming calls choose "registered SIP phone" (then our registration works) or "to your server via SIP" with the address of our PBX → with a number block, assign the base group number.

Pitfalls ⚠️ Incoming calls arrive on the registration name rather than on the number, so a line cannot be told apart by number (see "Numbers in the country"). Do not enable both modes at once: if you leave both the registration and the delivery "to your server", the call will arrive as two copies. Signalling and audio come not from a single address but from several provider networks — one more reason to choose registration rather than the IP mode. There is a single codec in their template, G.711 a-law, which suits us.

Source: VoIP SIP Trunks, VoIP Phones — Asterisk — 09.09.2026.

Voipfone#

A veteran of British small-business telephony: its own cloud PBX, cheap numbers and a support section for third-party PBXs with ready-made examples. A geographic 01/02 number costs £3 per month (£2.50 from the eleventh one), and a 056 number comes free on registration.

What to set up at the provider: buy or port a number → point it at the SIP account in the control panel → buy extra simultaneous channels if needed (they publish no channel table, so ask their support).

Pitfalls ⚠️ The provider says it plainly: phone numbers are not used at all in the third-party PBX configuration — the incoming call carries the account number. This means picking a line by number does not work on this trunk. Their examples list a single codec, G.711 a-law; check G.722 support when connecting.

Source: Asterisk Configuration Guide, Telephone Number Support — 09.09.2026.

VoiceHost#

A British carrier with its own network and 24/7 support; it has an article specifically about connecting Asterisk, which states plainly that the service works both with registration and with IP authentication.

What to set up at the provider: create an account → order a SIP trunk and the number of channels → receive the server address, login and password by email → add the numbers in international format (+441632960000) → in the IP mode, tell them the address of our PBX.

Pitfalls ⚠️ The server address is not published, so you cannot plan the connection without writing to the provider first — ask them using the list of questions from the overview. Only numbers from your account are allowed on outgoing calls. The codec in their template is G.711 a-law; they support encryption, but we neither need it nor mind it.

Source: Asterisk PBX SIP Trunk Configuration, 3CX SIP Trunk Guide — 09.09.2026.

Orbtalk / VoIPtalk#

Two brands of the same London company (Telappliant) sharing a help centre where ready-made trunk parameters are published.

What to set up at the provider: order the trunk and the numbers → set the outgoing number to one of those attached to the trunk → ask which server address is current and what arrives in an incoming call, the number or the login.

Pitfalls ⚠️ Two different server addresses in two articles of the same help centre are a classic cause of "registration is up but calls do not come". According to the current guide the incoming call carries the login, according to the older one the number: whether lines can be told apart depends on this. The codecs are G.711 in both variants, so all is well.

Source: FreePBX Guide — sip.orbtalk.co.uk, Orbtalk Settings for Asterisk — 09.09.2026.

Yay.com#

A young cloud PBX provider that openly supports a third-party PBX as well: the trunk parameters are published in its own help pages.

What to set up at the provider: create a SIP trunk in the account → attach the numbers to it → if needed, set the "incoming trunk name" so that the number format matches what is expected, and ask them to send the number in international format.

Pitfalls ⚠️ By default the incoming call carries the login rather than the number, so lines cannot be told apart by number. The codecs are G.711 in both variants plus GSM, so compatibility is there.

Source: How do I set up FreePBX to work with Yay? — 09.09.2026.

Wholesale carriers: Magrathea and Gradwell#

Both sell trunks to the communications business rather than to a venue, but their parameters are known, and this is the case where "the client already has their own carrier" happens more often than a self-service connection.

Magrathea#

An old wholesale numbering carrier, the "network underneath" many small British providers. The entry threshold: signed contracts and a first payment of £250 excluding VAT (a test account comes with £2 of credit). Both modes work.

What to set up at the provider: sign the contracts and pay the deposit → send them the static IP of our PBX by email for the whitelist → sign the agreement for presenting the number on outgoing calls → separately enable access to 999/112 if needed → point the numbers at our trunk.

Pitfalls ⚠️ Incoming calls arrive from six different addresses, while the trunk recognises the provider by a single server address: in the IP mode some calls may not be recognised — ask them to send from one address or use registration. Access to the emergency numbers is enabled as a separate upgrade: without it a 999 call simply will not go through. The number presented on outgoing calls must be valid and dialable — that is required by British communications rules, not just by the carrier.

Source: Client Handbook (PDF) — 09.09.2026.

Gradwell#

One of the first British SIP carriers (part of the Onecom group since 2025), certified by popular PBX vendors, priced from £4 per channel on request. The only mode is IP authentication.

What to set up at the provider: order the trunk and the channels → give them the static IP of our PBX for the whitelist → point the numbers at the trunk.

Pitfalls ⚠️ Without the whitelist the IP mode does not work at all, and changing the address of our PBX requires a request to the provider. Since the move into the Onecom group their knowledge base has relocated twice, so old links to the guides may not open and it is easier to request the parameters by email. The codecs and the number format are not publicly confirmed — ask them using the list of questions from the overview.

Source: Configuring an outbound SIP trunk on an Asterisk PBX, Gradwell SIP Trunks — 09.09.2026.

Providers that work by contract or through a partner#

International providers with UK numbers#

UK numbers are offered by every large international provider — DIDWW, Telnyx, Twilio, Plivo, Vonage, Bandwidth, Sinch, Infobip, Zadarma, VoIP.ms and others. Their parameters are taken from the account, and the cards for Telnyx, Twilio and Zadarma are already in the catalogue when adding a provider — the server address and the mode are filled in automatically.

• For a foreign company this is usually the only route. Local carriers require a UK address (sipgate says so directly, the others in practice), while international ones accept the customer's address and documents.
• Document checks are address-based. Twilio issues UK numbers through a regulatory bundle: proof of identity plus proof of an address in the same geographic area as the number's area code. The requirements of the others amount to the same thing.
• Modes. Telnyx offers registration or a connection by domain; DIDWW a static endpoint or registration; Twilio and Plivo work only by IP or by a credential list, with no registration at all; Zadarma uses registration to sip.zadarma.com.
• What international providers do not cover is the British paperwork: the address for the emergency services, the power-backup requirements and the porting procedure are still handled by whoever issued the number. If you plan to port an existing UK number to an international provider, ask in advance whether they support porting into the required geographic area.

Number porting#

• Both geographic and mobile numbers can be ported — the procedure is regulated by Ofcom. The request is submitted by the new carrier. Industry reviews put the typical timescale at about ten working days, with expedited porting taking one to three days; check the exact timescale in the contract of the particular carrier.
• A geographic number cannot be moved to another area: a 0113 number stays a Leeds number even if the carrier is in Bristol. For a chain of venues this means "a number per site" rather than "a number per brand".
• Porting out can cost more than joining. With sipgate it is £29 for the first ten numbers and £0.85 for each further one, and only all numbers at once can be moved, never a selection. Terms like these are worth reading before the venue picks a provider.
• Sign the contract in the name of the legal entity. With providers that allow online registration (sipgate, Voipfone, Yay.com) the contract is effectively signed by whoever registered: when the manager changes, the number leaves with that person.
• Take the analogue switch-off into account. If the number still sits on a telephone line or ISDN, porting it to a SIP provider is also a migration off the analogue network. Plan for a month rather than a week.

Rules and documents#

If it does not work#

1. Registration is up, calls arrive, but the line is not identified. The provider is sending the login instead of the number — that is how Voipfone, Yay.com, Orbtalk and Andrews & Arnold work. The call is still handled; to tell the numbers apart, ask the provider about number delivery or add a second trunk with a carrier that sends the number.
2. A call to the second London number follows the scenario of the first one. The 020 numbers share the last seven digits. Space the numbers out by ending when ordering, or handle both with one common routing rule.
3. Orbtalk: registration does not come up. The provider's help centre has two different server addresses in different articles. Try sip.orbtalk.co.uk, then talk.orbtalk.co.uk, and check with support which one was issued for your trunk.
4. Some incoming calls do not arrive in the IP mode. Andrews & Arnold and Magrathea send calls from several addresses, while the trunk recognises the provider by one. Switch the trunk to the registration mode — both of them support it.
5. One-way audio with Magrathea, Simwood, Gradwell or BT. The static IP of our PBX has not been added to the provider's whitelist. Take the address from the "Server" tab and send it to the provider; after a change of server capacity the address is kept, but it is worth checking.
6. A second simultaneous call does not get through. The plan has a single incoming channel (sipgate Starter) or is a two-channel product from another carrier. The number of channels is changed in the provider's account.
7. "Present as" is ignored on sipgate. The provider reads the presentation number from a separate SIP header that the PBX does not send by default. For now the trunk number will be shown; if you need to choose the number, write to our support.

Causes that do not depend on the country are in "If calls do not get through"; the network and codec requirements are in "Network and compatibility". A SIP trace in the trunk menu helps to analyse a particular call.

FAQ#

Can I get a UK number if the company is not registered in the United Kingdom?#

With local carriers, usually not: they require a confirmed UK address, and sipgate also posts a paper letter with an activation code to it. A foreign company will find it easier to buy a UK number from an international provider: there the customer's address and documents are accepted, although for a geographic number proof of an address in the matching area is often required.

Registration or IP authentication — which should I choose?#

Registration, if the provider supports it. British carriers often send calls from several addresses, while incoming calls are recognised by the single server address of the trunk: in the IP mode some calls may go unrecognised. The exceptions are Gradwell and BT Wholesale, whose only mode is IP-based, and there a whitelist with the address of our PBX is mandatory.

The provider sent a login instead of the number — is that a fault?#

No, that is how half of the British carriers work. The call is accepted and goes into routing as "a call from this provider", it simply cannot be matched to a line by number. With a single number at the venue nothing needs to be done; with several numbers, ask the provider whether number delivery can be enabled, or take a trunk from sipgate, VoiceHost, Voiceflex or Simwood.

How long does connection take?#

With sipgate it is 2–3 working days because of the paper letter with the code, and minutes of configuration after that. Voipfone, Yay.com, Orbtalk, VoiceHost and Andrews & Arnold take from hours to a day. Gradwell, Voiceflex and VoIP Unlimited take days, as an exchange of emails is needed. Magrathea, Simwood, BT and Gamma mean weeks and contracts.

How do I dial 999 through the PBX?#

You cannot: emergency numbers are shorter than four digits, while outbound rules in the PBX work from four. This is a deliberate limitation — an emergency call should not depend on an internet connection and a cloud switch. Keep a mobile phone on shift and check that the venue address in the provider's account is correct: that is exactly what goes to the emergency services.

Sources#

All links were checked on 09.09.2026.

Providers

• sipgate trunking — configuring Asterisk: https://teamhelp.sipgate.co.uk/integrations-and-connections/asterisk/how-do-i-configure-asterisk-for-sipgate-trunking · service specification, numbers and porting: https://www.sipgatetrunking.co.uk/service-specification · activation code by postal address: https://teamhelp.sipgate.co.uk/first-steps/quick-start-and-initial-set-up/start-code-for-sipgate-trunking
• Andrews & Arnold — VoIP SIP Trunks: https://support.aa.net.uk/VoIP_SIP_Trunks · configuring Asterisk: https://support.aa.net.uk/VoIP_Phones_-_Asterisk · signalling and audio networks: https://support.aa.net.uk/VoIP_Firewall
• Voipfone — configuring Asterisk: https://www.voipfone.co.uk/Asterisk_Setup.php · telephone number support: https://www.voipfone.co.uk/support/guides/numbers/telephone-numbers · prices: https://www.voipfone.co.uk/prices
• VoiceHost — configuring Asterisk: https://www.voicehost.co.uk/help/asterisk-pbx-sip-trunk-configuration · 3CX guide (number format, secure address): https://www.voicehost.co.uk/help/3cx-sip-trunk-guide
• Orbtalk / Telappliant — parameters for FreePBX: https://help.telappliant.com/en_GB/freepbx/freepbx-guide-siporbtalkcouk · parameters for Asterisk: https://help.telappliant.com/en_GB/asterisk/orbtalk-settings-for-asterisk
• Yay.com — configuring FreePBX and a SIP trunk: https://www.yay.com/faq/cloud-pbx/freepbx-config/
• Magrathea — Client Handbook (PDF): https://www.magrathea-telecom.co.uk/wp-content/uploads/2018/09/CLIENT-HANDBOOK.pdf · SIP trunking product sheet (PDF): https://www.magrathea-telecom.co.uk/wp-content/uploads/2021/04/Product-sheet-SIP-trunking.pdf
• Gradwell — SIP trunks: https://gradwell.com/sip-trunks/ · an outbound trunk on Asterisk: https://my.gradwell.com/s/article/configuring-an-outbound-sip-trunk-on-an-asterisk-pbx
• Simwood — Customer API v3 (PDF, number routing and codecs): https://cdn.simwood.com/docs/simwood_apiv3.pdf · partner trunks: https://simwood.com/2020/05/is-wholesale-right-for-you-simwood-partner-sip-trunks/
• VoIP Unlimited — SIP trunks: https://www.voip-unlimited.net/sip-trunks/ · BT Wholesale — wholesale SIP trunking: https://www.btwholesale.com/products-and-services/hosted-communications/wholesale-sip-trunking.html · Gamma — SIP trunking: https://gammagroup.co/products/sip-trunking-call-management/

Regulator

• Ofcom — calling line identification (General Condition C6): https://www.ofcom.org.uk/phones-and-broadband/phone-numbers/calling-line-identification · general conditions of entitlement: https://www.ofcom.org.uk/phones-and-broadband/telecoms-infrastructure/changes-general-conditions-of-entitlement
• Ofcom — the national telephone numbering plan (PDF): https://www.ofcom.org.uk/siteassets/resources/documents/phones-telecoms-and-internet/information-for-industry/numbering/other/national-numbering-plan.pdf · access to emergency organisations during a power cut: https://www.ofcom.org.uk/phones-and-broadband/telecoms-infrastructure/access-emergency-organisations-power-cut · letter to businesses on the PSTN switch-off deadline (PDF): https://www.ofcom.org.uk/siteassets/resources/documents/consumers/2024/published-letter-to-business-on-pstn-switch-off-deadline.pdf

Secondary sources

• Enreach/Swyx — Voiceflex interoperability report (codecs, number format): https://service.swyx.net/hc/en-gb/articles/10532412766108-SIP-Provider-VoiceFlex-UK · 3CX — configuring a BT WSIPT trunk (registerless mode): https://www.3cx.com/docs/sip-trunk/bt-wsipt-uk/
• Twilio — regulatory requirements for UK numbers: https://www.twilio.com/docs/phone-numbers/regulatory/reading-regulations-for-the-uk-bundle · Connection Technologies — UK number porting timescales: https://connection-technologies.co.uk/blog/voip-number-porting-uk-2026-how-it-works-timelines-paf-cost

Related pages#

• Connecting a provider number to the PBX — the common steps, trunk modes, network, testing.
• Setting up SIP phones — how to connect desk phones and DECT handsets to extensions.