I'm glad you brought up gv mobile it was I think once on the Android market, didn't know it was on app store for apple.
In terms of linphone not ringing, it should ring, when u do a test call to your Google voice number it should ring your linphone sip client. If that happens it should also happen for when the call back is being placed by gv mobile.
In regards to really good sip phones for iPhones, I really don't know that many b/c I am use to Android and the famous sip phone for Android is sipdriod, which is really great, as its been out for a while and they have sipdriod intergrated with Google voice, but in terms of apple and ios I think the best sip phone would be linphone. You might have to just be the enduser that tells the developers, what enhancements and bugs are going on in an iPhone, and what u are trying to accomplish with linphone; in order to improve linphone.
Nikolai Gauntlet Cassanova
SUNY University at Albany
Bachelors of Science in Biology
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