Session Initiation Protocol (SIP) is a signaling protocol for initiating, terminating and modifying user sessions over an IP network.
Using SIP to connect to Twilio is one way to get access to Twilio's global reach and powerful automation and scripting functions.
It's easy to connect your on-site or virtual Private Branch Exchange (PBX) with Twilio's servers. Here's our overview of connecting your existing SIP communications infrastructure to us.
For information about SIP Trunking with Twilio, check out our Elastic SIP Trunking documentation.