A SIP trunk is, in short, the “phone line” of a modern phone system — except it runs over the internet, not copper cabling. It connects your phone system (PBX) to a carrier so you can make and receive calls to the public network. Here’s what you need to know, jargon-free.
How it works
Classically, a business had physical lines or ISDN circuits from the carrier. A SIP trunk replaces them with a digital connection: your system speaks the SIP protocol (the standard for internet telephony) with the carrier, and calls travel as data. A single trunk can carry dozens or hundreds of simultaneous conversations.
Why it matters
- Cost — usually cheaper than classic lines, especially for long-distance and international calls.
- Scaling — add or remove channels without pulling new cables.
- Numbers — keep your existing numbers (by porting) or get new ones, including geographic.
How many channels you need
A “channel” = one simultaneous conversation. The simple rule: estimate how many calls happen at peak, at the same time — not the number of employees. A team of 50 rarely has 50 simultaneous calls; often 10–15 channels cover the peak. A traffic test clarifies the exact figure.
Compatibility: you’re not tied to one carrier
A key advantage of standard SIP: any SIP-compliant phone system connects to any SIP carrier. You aren’t tied to the trunk provider — you can switch carriers while keeping your system, numbers and phones. That’s the opposite of a proprietary solution that locks you in.
How it relates to Pentacomm
Pentacomm speaks standard SIP end to end, so you can use your preferred carrier (register, auth or peer mode), with ordered failover across trunks and per-trunk caller-ID rules. You bring your own trunk; we don’t sell you minutes or tie you to a particular provider. See how it fits into the platform or read about what “no vendor lock-in” means.