SIP trunks enable the use of VoIP services that are provided by carriers or service providers. The service provider provides you with a phone number or a number range. Alternatively the SwyxWare users can be assigned SIP addresses (SIP-URIs, e. g. "tom.jones@swyx.com") by the provider, which can be used as an "email address for a telephone". By this means, SwyxWare users can globally reach other SIP-URIs, and be reached themselves. If this service provider also offers gateway services, it will also be possible to reach any phone in the public telephone network via an SIP trunk and the underlying gateway of the provider.

An SIP trunk connects the software-based telephony system to a service provider, e.g. a SIP-ITSP (Internet Telephony Service Provider) or SIP provider for short (e.g. 1&1, outlook.com, GMX, etc.). Call connections are created and terminated via SIP (Session Initiation Protocol) as a communication protocol.

In SwyxWare, the connection is configured as a SIP trunk or SIP trunk group.