If you need a spare phone or if you're a developer looking to pick one for cheap, then you can't go wrong with the Nokia Lumia 520. Amazon has a lightning deal (only 4 hours) with the device, selling it for $44.99. That's pre-paid, no contract, meaning you owe nothing to AT&T.
For $45 this is a great little phone to have kicking around (or developing apps on). Don't forget, you can even put Windows Phone 8.1 on there today! (For those asking, yes, the Lumia 520 is carrier SIM locked to AT&T. In theory, you can unlock it, but AT&T can be difficult. You can always try their site.)
Head here to grab the deal, but remember you only have a few hours! http://phon.es/520deal