3gs running non iphone sim card

[cavids]

I am getting ready to upgrade my wife's 3g to a ipone4, I was wondering both my kids have normal att phones, with voice and text service, but no internet. Is it possible to just run one of their sim cards in the iphone 3gs and not tell att, I realize that they will not have 3g service for internet as they do not have a data plan. but they do not have it now anyway, on the flip side they would have internet when they were at home with wifi?

[z3r01]

Well :

1. Your posting in the wrong section
2. Once you put the sim card in, AT&T will kno an update your plan