Not sure if this helps anyone but just noticed that with the AT&T sim that comes with the iPhone (but not unlocked - I'm in the UK) the Settings screen allows you to use the Carrier sub-menu (under Wi-Fi) to select a UK carrier. Obviously it doesn't work with an unactivated AT&T sim!
But if I put my T-Mobile UK sim in the phone, the Carrier option disappears and is missing from the Settings screen.
Don't really know if it means anything to anyone who's working on an unlock but I just thought I'd mention it.
Yea i had my AT&T sim in i had turned off my phone and turned it back on and i went to settings and i saw the carrier menu for the first time....so i left my phone alone for awhile and i went back into settings and it was gone...so.....idk. So get back at me if u know anything about it.