SIP Trunk in United Kingdom — London, Manchester or Edinburgh Inbound + Outbound

1. What a SIP trunk in United Kingdom actually is

A SIP trunk is the IP delivery pipe between a carrier and your PBX, AI voice agent, or call-control platform; signaling over SIP, audio over RTP. A United Kingdom SIP trunk is the same thing carrying +44 UK DIDs allocated under Ofcom.

DIDHub provides the trunk authentication and SIP transport; Ofcom-compliant number allocation is coordinated through our in-region carrier partners. Your PBX or platform sees a standard SIP trunk; we handle the regulator-side paperwork.

2. United Kingdom regulation: Ofcom, KYC, compliance

Ofcom doesn't require KYC for standard United Kingdom number allocation. Activation is Instant.

What people typically use a United Kingdom SIP trunk for:

• UK market entry, a London 020 number on your sales line dramatically outperforms a foreign Caller ID for UK B2B.
• Regional credibility, Manchester 0161, Birmingham 0121, Glasgow 0141, or Edinburgh 0131 numbers signal local presence.
• Non-geographic 03, charged at the same rate as 01/02 by Ofcom rules; useful for centralised customer support with no regional bias.
• Toll-free 0800/0808, free for UK callers, standard for premium customer service.
• AI voice agents targeting UK, London ingress + UK Caller ID gives noticeably better answer rates than international IDs.

The UK regulator Ofcom does not require KYC for standard geographic, 03 non-geographic, or 0800 toll-free allocation. Activation is instant. Inbound SMS is supported on most numbers; outbound commercial SMS requires registration with the carrier. The UK is the standard light-regulation European market for VoIP setup, making it the easiest European country to establish a local presence.

For the broader picture across countries, see our guide to international DID compliance & KYC bundles. For the SIP-trunk concept end-to-end, see the DID Number Provider guide.

3. Number types you can route over the trunk

DIDHub supports the standard United Kingdom number types over the SIP trunk:

For a deeper look at how number types differ globally, see DID number types explained.

4. How DIDHub's SIP trunk works in United Kingdom

The technical surface of the trunk is standardised; the United Kingdom-specific choices are the POP, the codec list, and the failover topology.

Ingress POPs

• London (primary), lowest in-region latency to United Kingdom endpoints.
• Frankfurt (failover), secondary route used if the primary path degrades.

Transport & security

• TLS:5061 recommended for any production trunk; UDP allowed for legacy.
• SRTP for media via DTLS-SRTP or SDES.
• SIP authentication: digest registration (PBX behind NAT) or IP-ACL (static peering). See SIP authentication.

Codecs

• G.711 a-law (PCMA), the European default.
• G.722, wideband HD voice on capable endpoints.
• Opus, for AI voice agents and IP-native softphones.
• G.729, available on request.

For the codec deep-dive, see voice codecs explained.

DTMF

• RFC 4733 (telephone-events over RTP) is the default. SIP INFO and in-band DTMF available for legacy interop on request.

Channel concurrency

• Trunks start at 5 concurrent channels and scale to 200 per trunk off the shelf. Larger requires a custom arrangement.
• Channels are independent of DID count; you can carry 200 numbers on a 10-channel trunk if your concurrent-call peak is 10. See multiple concurrent calls on one DID.

STIR/SHAKEN

• Not applicable. The North-American STIR/SHAKEN attestation framework is a US/Canada construct that doesn't exist in Europe. EU trust signals come through national regulator registration and operator-side caller-ID validation.

5. Outbound calling from your United Kingdom trunk

Outbound from a United Kingdom-allocated DID to United Kingdom destinations is allowed within approved use cases. The per-minute economics:

Outbound caller-ID rules

• Your outbound CLI must match a DID you've allocated through the trunk. Setting an arbitrary caller ID is rejected at the SBC.
• Origin-based rating (OBR) applies on cross-border outbound, the regulated EEA tier may apply depending on the source carrier.
• For multi-region operators, see origin-based rating savings.

6. Setup in 6 steps

Asterisk pjsip example

; /etc/asterisk/pjsip.conf
[transport-tls]
type=transport
protocol=tls
bind=0.0.0.0:5061
cert_file=/etc/asterisk/keys/asterisk.crt
priv_key_file=/etc/asterisk/keys/asterisk.key
method=tlsv1_2

[didhub-united-kingdom]
type=auth
auth_type=userpass
username=YOUR_DIDHUB_USERNAME
password=YOUR_DIDHUB_PASSWORD

[didhub-united-kingdom]
type=aor
contact=sip:sip.didhub.io:5061;transport=tls
qualify_frequency=30

[didhub-united-kingdom]
type=endpoint
transport=transport-tls
context=from-didhub
disallow=all
allow=g711a,g722,opus
outbound_auth=didhub-united-kingdom
aors=didhub-united-kingdom
dtmf_mode=rfc4733
media_encryption=sdes
direct_media=no

3CX SIP trunk template snapshot

# 3CX -> SIP Trunks -> Add SIP Trunk -> Generic SIP Trunk
Trunk name:        DIDHub United Kingdom
Registrar:         sip.didhub.io
Transport:         TLS
Port:              5061
Authentication:    Register/Account based
Auth ID:           YOUR_DIDHUB_USERNAME
Auth password:     YOUR_DIDHUB_PASSWORD
Outbound caller ID: +44 ... (one of your allocated DIDs)
Codecs (priority):  G.711a / G.722 / Opus

7. Integration patterns

Every modern PBX, UC platform, and AI voice stack can authenticate against the trunk:

8. Pricing

Four line items: per-DID monthly rental, per-minute inbound usage on every United Kingdom DID (even landline geographic numbers carry an inbound MOU charge in United Kingdom), channel capacity, and per-minute outbound. Setup is $0 once Ofcom paperwork is approved.

Per-DID monthly

Channel capacity

Per-minute outbound

See section 5 above and the full global rate sheet.

9. Porting an existing United Kingdom number

Existing United Kingdom number? Porting timeline is 2-4 weeks.

• Typical port time: 2-4 weeks
• Required documents: phone bill + LOA + ID + proof of address (Ofcom requirements)
• Cost: port-in fee per number; carrier-side fees may apply

For the full porting playbook (US/UK/EU + the global gotchas), see number porting explained.

10. FAQ

Which POP should I connect to for a United Kingdom SIP trunk?

London is the recommended primary; Frankfurt is the standard failover. Both terminate to United Kingdom via in-region carriers.

How long does activation take for a United Kingdom SIP trunk?

Instant after KYC documents are accepted (or instantly where KYC isn't required). Provisioning the SIP side itself is hours, not days; the variability is on the Ofcom/carrier side.

What codecs should I configure for a United Kingdom SIP trunk?

G.711a / G.722 / Opus as the negotiation list, in that order. G.711a is the regional default for United Kingdom interop.

Can I use my United Kingdom SIP trunk with Microsoft Teams?

Yes, via Microsoft Teams Direct Routing through DIDHub's managed SBC. See Teams Direct Routing.

Can I use my United Kingdom SIP trunk with AI voice agents (Vapi, Retell, ElevenLabs)?

Yes, BYOC SIP trunk works with every major AI voice platform. Bind specific United Kingdom DIDs to specific agents; outbound CLI must match an allocated DID.

How many concurrent calls can one United Kingdom DID handle?

The DID is an address; concurrent-call capacity is set by the channel count on the trunk. A 50-channel trunk with 1 DID can carry 50 concurrent calls to that one number; the same trunk with 200 DIDs can carry 50 concurrent calls across any combination of those numbers.

Does STIR/SHAKEN apply in United Kingdom?

N/A (regional construct). Trust signals come instead through national regulator registration and operator-side caller-ID validation.

Can I port my existing United Kingdom number to a DIDHub SIP trunk?

Yes. Typical United Kingdom port timeline is 2-4 weeks. Required documents vary by number type; contact us for the specific checklist. See number porting explained for the global picture.

What use cases get approved most easily?

Customer service inbound, opted-in callbacks, transactional 2FA, inbound AI voice agents, and Microsoft Teams Direct Routing for registered entities. Cold outbound, unsolicited SMS campaigns, and anonymous-relay setups are routinely rejected.

11. Related country pages