I have a 3GS and my old original iphone is collecting dust.  My GF is already a ATT subscriber.  I just went into an ATT store, and was told that I can just put her sim card in my old iphone, go through the activation, and everything would be fine.

 

The question he didn’t really answer was: Will she be able to upgrade to a new phone (4th Gen Iphone) and get the contract extension discount? 

 

Also I keep reading that you need to put a new sim card in the old iphone for it to work, this true? the guy at the store told me her current sim card will work (she has a 3G phone).

 

Thanks!