Key takeaways
- SIP trunks carry calls over the internet instead of copper lines
- You can add or remove channels without new cabling
- A dedicated or prioritised internet link protects call quality
- Keep a failover route so calls continue if the link drops
Many offices still pay for a bundle of traditional phone lines connected to their PBX. SIP trunking does the same job over your data connection, usually for less money and with far more flexibility. For most businesses moving to an IP phone system, it is the natural next step.
What a SIP trunk is
A SIP trunk is a virtual phone line delivered over the internet or a private data link. Your IP PBX or cloud phone system connects to the provider, and each trunk can carry a number of simultaneous calls, called channels. Your existing numbers can usually be kept.
Why businesses switch
The main benefits are cost and control:
- Pay for the number of channels you actually use
- Add capacity for busy seasons in days, not weeks
- Route numbers to any branch or remote worker
- Lower call rates, especially between sites
- One provider for numbers across several locations
How many channels do you need?
Channels are not the same as phones. Ten staff rarely make ten calls at once. Look at your busiest hour from current call records and size for that, plus some headroom. Call centres need a closer calculation because most agents are on calls at the same time.
Protecting call quality
Voice needs a stable connection more than a fast one. Use quality of service on your router so voice traffic goes first, avoid running calls over a congested shared link, and consider a dedicated internet line for larger phone systems. Jitter and packet loss matter more than download speed.
Security and fraud
SIP trunks are a target for toll fraud, where attackers place expensive international calls through your account. Lock down the PBX, restrict international destinations you don't call, set spending alerts and only allow connections from your provider's addresses.
Planning the move
We review your current lines, call volumes and network, then plan number porting, failover and PBX configuration so the switch happens with no missed calls. Talk to us for a free assessment of your phone lines.
Frequently asked questions
In most cases yes. Numbers are ported to the new service and the switchover is scheduled to avoid downtime.
Older PBX systems may need a gateway or an upgrade. Most modern IP PBX systems support SIP natively.
Calls can fail over to a backup link, mobile numbers or another site, depending on how the system is set up.
No. A SIP trunk replaces your lines. A cloud PBX replaces the phone system itself and usually includes the lines.
