Linphone

Linphone is an open source internet SIP phone or Voice Over IP phone (VoIP) WIFI/3G, with video calls support for ARMv7 phones.

Main features:
-Audio with the following codecs: speex (narrow band and wideband), iLBC, G711, GSM
-Video with mpeg4 and H264 codecs (ARMv7 only)
-Echo cancellation
-Address book integration
-Call history