📞 What is SIP Trunking?
A SIP trunk is a virtual phone line that runs over your internet connection. Instead of plugging physical telephone cables into a wall socket connected to BT's network, SIP trunks send your calls as data packets over your broadband.
The "SIP" stands for Session Initiation Protocol — the technical standard that controls how voice calls start, connect and end over IP networks. The "trunk" is an old telecoms term for a group of lines (traditionally a bundle of phone lines connecting an office PBX to the public network).
🔄 SIP Trunk vs Hosted VoIP — What's the Difference?
This is where most people get confused. Both use the internet to make calls, but they work differently:
| SIP Trunks | Hosted VoIP | |
|---|---|---|
| What you provide | Your own on-premise PBX hardware | Nothing — it's all in the cloud |
| Monthly cost per channel | £3–£8 | £10–£20/user |
| Setup complexity | High (PBX config required) | Low (plug and play) |
| Best for | Businesses with existing PBX | New setups or PSTN migration |
| Hardware required | IP-compatible PBX | IP phones or softphones only |
| Scalability | Add channels manually | Add users instantly |
🎯 When Does SIP Trunking Make Sense?
- You already have a working on-premise PBX (Avaya, Cisco, Panasonic, NEC) that you want to keep. SIP trunks replace your ISDN lines without replacing the whole system.
- You have high call volumes where per-channel pricing is cheaper than per-user hosted VoIP.
- You need PSTN migration ahead of the 2027 switch-off but aren't ready to replace your PBX yet.
- Your PBX has features (complex hunt groups, operator consoles) that would be costly to replicate in hosted VoIP.
💷 SIP Trunk Pricing in the UK
| Channels | Monthly Cost | Included Minutes |
|---|---|---|
| 2 channels | £15–£25 | Unlimited UK calls |
| 5 channels | £30–£50 | Unlimited UK calls |
| 10 channels | £55–£90 | Unlimited UK calls |
| 20 channels | £100–£160 | Unlimited UK calls + CLI routing |
A "channel" = one simultaneous call. For most offices, you need roughly 1 channel per 3–4 users for typical call patterns.
🔧 Will SIP Trunks Work with My Existing PBX?
Most modern IP-capable PBX systems support SIP. However, if your PBX was installed before 2010, it may not support SIP without an adapter (ISDN gateway). Before ordering SIP trunks, confirm with your PBX supplier or installer that the system is SIP-compatible.
Telexico provides SIP trunks for businesses across the UK, with number porting included. Get a quote in 24 hours.
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