ZOIPER 2.0 Free SIP and IAX is a user-friendly softphone, compatible with Asterisk or any other SIP or IAX capable system. High-quality VoIP experience with features like: SIP + IAX protocols, SIP over TCP / TLS / UDP with STUN support, Echo cancellation, DTMF tones, Multiple audio devices support, Automatic user registration, Call transfer, Hold function, Multilanguage support, Portable storage compatibility, Codecs: GSM, ulaw, alaw, speex, ilbc