Lumicall is an open source Android softphone. It only supports audio and does not support video or messaging yet. It has good support for SRTP and ZRTP encryption, uses SIP over TLS and supports ICE and TURN for NAT busting.

Summary

SIP profile/account setting screenshots

lumicall-config-1.png lumicall-config-2.png lumicall-config-3.png

Dialing a number with your Debian account

lumicall-dial-test.png