The banning of GV is more to do with AT&T phobia than with Apple I believe in this case. This is because It allows users to send free SMS messages and get cheap long-distance over Google Voice. It also makes it trivial to switch to a new phone service, because everyone calls the Google Voice number anyway and hence you don't have to depend upon number portability and all such.

The same could happen with Nokia phone if release with AT&T. Of course there is the plus side that you could always but the phone unlocked and do anything with it. That's an advantage of Nokia.

But seriously nobody even in my friends circle (tech friends) even know what GV does or are impressed with it. They always say - "but why do I need GV on my phone, I can already make calls from my cell."

And open or closed has never been a factor in who sells a product the most in most consumer markets.