I know this is old, but here's an update.

You can buy a SIM from Straight Talk at [Only registered and activated users can see links. ] for $15 and it will work with any and all AT&T phones.

Not only will you get Edge, and 3G, but you'll get 4G in 4G coverage areas, as well as free roaming on T-Mobile.

Also, you can cut the SIM down to nano-sim size to work in the iPhone 5.