I've got an extra upgrade on my At&t family plan and nobody in my family wants to use it. My girlfriend who has a 4 on her own plan wants a 4S so I was thinking about using one of my upgrades to get it for her. But do I have to activate it when I order it under my sister's phone line and subsequently killing her phone? Or can I just pop out the SIM card when I get the phone and put my GF's card in it? I don't live in the same state as the rest of my family so if I end up killing my sister's access to her phone and putting her line on my GF's new phone before swapping the card that would be disastrous for my sister, she lives on the phone... used over 700 text messages in the last 6 days... so she won't be able to go even a single day without her phone if I were to next day the SIM card back to her. To the point... can I get an upgrade for my phone and not activate the phone on the account I bought it for?