Android Sip Client

From VoIP.ms Wiki

This guide is based on the native Android SIP Client that is included with Android 4.1.1. We cannot guarantee 100% compatibility with all future Android releases since settings may change. This guide is provided for those who wish to experiment, and probably use, this software. Ideally you will want to use a wifi connection with these features, instead of a 3G connection.

NOTE: Please be aware that: If used over 3G/EDGE then depending on carrier and service plan used, you may be billed for your data usage.