Upgrade original iPhone (edge only) with 3GS from eBay

[Jeanne8fr]

Hello all,

We have an old iPhone with the unlimited data plan. We are thinking of buying a 3GS and pop the old sim card in it. I know that AT&T knows when you are using an iPhone but will they also know that it was updated?

Thanks,

Jeannette

[Cer0]

Some people say that going from 2g unlimited and putting it in a newer iphone somehow tricks the system to give you 3g unlimited still.

[John1177]

If you have an unlimited plan you are grandfathered in to the unlimited plan as long as you have an iphone, no matter how many times you upgrade.