I began to study the VOIP/SIP agreement from 09, open source project also saw a few, the earliest Pjsip 05 began to push the time, began to pay attention to, also in their own winmobile project used. Later also saw Sipdroid,imsdroid (Doubango), Linphone,csipsimple (PJSIP).
I think the best advantage of Linphone and Csipsimple,linphone is the full platform support, Android,ios,winphone,windows,linux,mac osx,web all support, but the quality is still under the heat, Changed his library, added the support of g.729, his C code, naming and indentation are all confused.
May be I have seen Pjsip code, some sentiment has a single clock, in short, I very much like pjsip concise, efficient, code design is very good, note document is also great, directly with Doxygen to generate documents. So nature pays special attention to some csipsimple.
On the UI, Csipsimple basically extracts the Android native dialer and then uses the interface generated by Swig. The integrity of the functionality, or the UI is more than the other open source. So I made a lot of improvements on Android, mainly based on Csipsimple. Enjoy several interfaces:
Please refer to: VoIP network telephony based on csipsimple development Icaller for Android
Android Internet telephony development, VOIP/SIP so many open source choose which good