Key details

NAT traversal

Jitsi configuration

JSCommunicator

Just take it from upstream github, use the web-phone package and symlink the files to your own web directory or clone an existing site:

mkdir /var/www/jscommunicator
wget -nH -r http://debrtc.org
vi config.js

Lumicall

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