SIM cards for iphone 4 and 4S questions

[achtungfemme]

(1) Is it possible to just take the sim card out of an old iphone 4 and put it in an iphone 4S and use it? They are the same size correct?

(2) Will At&t count that as an upgrade? Or will they not even really know about it?

(3) Do iphone 3GS's and Iphone 4S's have different sized SIM cards? If you get a used iphone 4S can you take the sim out of a 3GS and put it in a 4S? Or do you need to contact AT&T for a new SIM card? And if you do that will they count that new sim card as an UPGRADE?

Thanks for your help!!

 

[MacManTexas56]

(1) Is it possible to just take the sim card out of an old iphone 4 and put it in an iphone 4S and use it? They are the same size correct?

(2) Will At&t count that as an upgrade? Or will they not even really know about it?

(3) Do iphone 3GS's and Iphone 4S's have different sized SIM cards? If you get a used iphone 4S can you take the sim out of a 3GS and put it in a 4S? Or do you need to contact AT&T for a new SIM card? And if you do that will they count that new sim card as an UPGRADE?

Thanks for your help!!

1- yes they both use a micro sim
2- no, upgrades only count when you buy a new device from them. they will know about it and it will show up on your account but it won't affect anything.
3- 3GS has a regular size sim card, you can get a sim cutter that will cut it to fit a 4 or a 4s. Upgrade is only referring to buying equipment through them. You don't have to sign a new contract if you bring your own device.