well i was thinking. the turbosim emulates being ATT at those 2 requests the phone makes. so far i know those are the only ones. after this part, the your normal none att sim takes over again.
so my idea is if its just to about those two checks if its an att card, couldnt it be possible to start up the iphone normaly with you att sim so he can make his checks on the sim and after that some app would freeze the whole iphone. you then take out the att sim and put in your own sim without the iphone noticing. after this is done you can "unpause" you iphone again and it will continue working with your own sim card.
this is basically all turbosim does and it should be possible because the iphone doesnt randomly check the sim card, just those two first times.
the problem here is how to freeze and unfreeze the phone.

any ideas?

you gonna get flammed

inshort, if it could be "that simple" it would have been done already

the method you descibed is what supersim and turbo sim and the new hypercard do....

Seriously, how you want to stop the RTOS on the baeband to notice simout simin? You can freeze the apple crap as long you want, bb has its own OS.