I'm not sure exactly how the tech works, but if GV works over the data network, similar to skype, I'm concerned the quality, connection time, and amount of dropped calls would be worse than a regular call. The iPhone drops enough calls as it is, I imagine it could get much worse if the phone had to open an app, third-party or not, and place calls over the data network.

And what about SMS? For me to use GV full time, I need the ability to send SMS's from my GV number. MMS as well. I hope this functionality will be built into the app, if one ever makes it to the device.