Can I use your service with VoIP ? callbrix.com has support for SIP based VoIP phones. Connecting VoIP phones - Yes, we support connecting VoIP phones. See User Extensions. 3rd party SIP trunks - No, we do NOT support connecting to 3rd party VoIP service providers for outbound call termination. 3rd party DID's - No, we do NOT support receiving SIP calls from 3rd party VoIP/DID service providers.