I just switched over to Straight Talk (working fine, including the MMS, although I had to pay five bucks for a jailbreak app called TetherMe to update the settings). I also ordered a replacement battery and screen (mine has a couple of scratches in it) this week. If I get all those on and everything works as it should (I don't foresee any problems) essentially I'll have a brand new 4S on monthly service with unlimited talk/text/data and will be telling ATT to go take a long leap off a short pier. Should know for sure next week (this weekend I'll be sitting down to disassemble the phone and swap out all the pieces). If I can't get everything back together then I'll buy a iphone 5.
win-win for me.