If you are looking for a good SIP (VoIP) client for your Android, there are two workable and functioning well clients available. They are all released under GPL, CSipSimple and SIPDroid.

CSipSimple vs SIPDroid

- CSipSimple is almost fully integrated to Android's dialer and call logs. You will be very happy when you dial out. You will ask if you are going to dial out via SIP or GSM. However, SIPDroid does not.

- CSIPSimple does not support Video streaming over IP (it is because it is still under Alpha stage). SIPDroid is supported (beta at the moment).

- Both of them are compatible with Asterisk. CSipSimple provides wizard to configure Ekiga and other common providers in the world. It is much easier than SIPDroid. SIPDroid is easier for configuration to PBXes.org.

Sounds good?! I would like to share a tutorial to you all.

(a) HOWTO : Voice over IP (VoIP) on Android (Asterisk Edition)
(b) HOWTO : Voice over IP (VoIP) on Android (Ekiga Edition)

Enjoy!

Samiux