Once you have activated the phone on the upgraded line and agreed to the new contract, you can do whatever you want with the phone. You could sell it on Ebay if you wanted or use it on a friend's account. It's your phone.

pros6592 said:
Suppose I get a new phone on a ne2 upgrade. Do I have to use that phone with the associated line or can i switch the phones that are associated with two lines

Get the phone activated on the line the NE2 was granted for and then call into Cust Serv to have the ESN's swapped. It's no big deal.