it won't work, I have posted on this before (It'll be just like Blackberry BIS logins that are network specific)
The key to it all is iTunes activation, you have to go through the Apple iTunes activation servers and they simply lookup your IMEI and match that in a table against which operator it was destined for. If you buy it in New York that will be AT&T, but it in London, it'll be O2.
No multiple hardware versions required, just a database table column on the iTunes activation servers.