I remember reading here when iOS 7 was in beta that you could no longer do the SIM swap trick to enable data and MMS on Straight Talk. Basically what happens is when you remove the T-Mobile SIM, you get a 'No SIM' error message and get kicked out of the Cellular settings page, which then disappears after you've put in your Straight Talk SIM. I forgot about that, and updated to iOS 7 GM last night. After updating, my data and MMS stopped working, so I tried SIM swapping... What I found is that the trick still can work, but it's just harder to pull off. You have to be really fast when removing the T-Mobile SIM and putting in your ST SIM. No time to fumble around, flipping the SIM card over, etc.- or else the error message will kick you out. But after a few tries, I was fast enough to stick the ST SIM before getting the error, so the phone stayed on the Cellular settings page and was able to change the settings. So it is possible- just keep trying. I was able to do it with 2 4S's last night. If you have an extra SIM tray then the job will probably be much easier, you can then pop out 1 tray and quickly stick the 2nd tray with your ST SIM already in it.