I don't have Straight Talk, but I have Net10 which is pretty much the same thing. I use an AT&T SIM card and it works very well in my iPhone 5. The only issue I've had is that MMS doesn't work, and based on my research it seems MMS isn't possible without jailbreaking. It's not my main phone so it's not a big deal to me, otherwise I would have to do something about it.