Alright, here is the deal: My wife and I bought ATT phones with a 2 year agreement, 2 years ago. Sadly, my phone recently died. I didn't want to sign up for another 2 years, and of course I didn't want to buy a new phone at full price. So... What did I do?
I went into my local Radio Shack (none of those lines typical at AT&T stores) and told them that I'd like to buy a prepaid AT&T phone as a gift for a friend. This way they didn't ask me if I wanted to buy any phone cards for it. I paid $10 for a new phone - opened it up, put my old sim card into it and continued on my old plan as if nothing ever happened. That's not all:
As a bonus, they include a sim card. Now if you have ever had to buy a sim card to replace your old one, you know that they cost $25. So, what you do is you keep this one (even though it is currently set up to be a 'pay as you go' sim card) and if you ever lose your sim/phone they can activate that one with whatever plan you desire.
How did I learn this? A very very kind hearted employee gave me the run down a few days back.