Receive VoIP call via Google Voice => IPKall => Sip2Sip => Android?
You can use sipdroid, released under GNU GPL v3, also available from Google Play Store and save yourself a lot of trouble.


  sipdroid is a free SIP/VoIP client for Android.


As for a SIP provider, Sipgate for example gives good results for both outgoing and incoming calls.

From version 2.0


  For Google™ Voice users, Sipdroid can now create a new, free PBXes account that is automatically linked to an existing Google™ Voice account. The new feature requires Android 2.0, or above, and Google's app connected to your Voice account.


Download the current version Sipdroid-2.7.apk available since May 21, 2012.

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