Based on SIP (Session Initiated Protocol)
a SIPphone is a SIP service that provides a free SIP-based VoIPnetwork. To use SIPphone you need either a SIPphone adapter or
softphonesoftware and a
broadbandInternet connection. To make free in-network (SIP to SIP) calls,
both sides of the call must have a SIPphone adapter or softphone. To make
inexpensive calls to non-SIPphones (PSTN), you will need SIP minutes.