SIP trunking — Session Initiation Protocol trunking
What is SIP trunking?
SIP trunking connects a business phone system — an on-premise PBX or a cloud UCaaS platform — to the public telephone network over a SIP (Session Initiation Protocol) connection instead of physical phone lines, so calls travel as data over an internet connection. It lets a company keep its existing PBX and phone numbers while modernizing how calls reach the network, scale call capacity up or down by adding trunks, and consolidate multiple office lines under a single connection.
More detail
A SIP trunk is authenticated either by registration (username/password) or by IP allow-listing, and typically carries a configurable number of concurrent call channels rather than a fixed set of physical lines.
Bring-your-own-carrier (BYOC) SIP trunking is the common pattern for keeping an existing carrier relationship and numbers while adopting a new call-handling platform's IVR, queues, and reporting.
Frequently asked
- Do I need new phone numbers to use SIP trunking?
- No. SIP trunking is commonly used to keep existing phone numbers and carrier relationships (bring-your-own-carrier) while changing only how the call signaling reaches the network — numbers port or forward onto the trunk.
- How is a SIP trunk different from a traditional phone line?
- A physical phone line carries one call per line over a dedicated circuit. A SIP trunk carries calls as data over an internet connection and typically supports many concurrent calls on one trunk, with capacity adjusted by configuration rather than wiring.
See also
Build it on Orbit
Voice, messaging, email, video, and AI agents on one platform and one pay-as-you-go bill. Start free — no credit card required.