sip stack for iphone and android

I am looking for the SIP stacks for Android and iPhone. I found plenty of similar questions, which are sometimes quite old... I do not care too much if the solution is commercial (but this is preferred) or open source.

So far I found

• Commercial solution from RADVISION for Android
• Open source SIPHONE for iPhone
• LINPHONE which covers both platforms.
• Gingerbreadhas built-in SIP stack - but seems that it has some limitations and might be removed by MNO...

My questions are:

1. Does anybody has good/bad experience with above solutions?
2. Do you develop and publish an application with use of above solutions?
3. Any commercial SIP stack provider for iPhone/iPad?

Thanks a lot STeN

RADVISION, the company I work for, which you have mentioned offers its SIP stack also for iOS (which translates to iPhone and iPad). Can't say how good it is (I can, but I don't think it matters what I think about our solutions), and we do have customers who have used our products successfully on these devices.