Apparently you can bring up the APN settings without being jailbroken if you plug in a T-Mobile SIM, open Settings, navigate General -> Network, and open the "Network settings" menu that appears when an unrecognized SIM is entered. Then, put the StraightTalk SIM into the iPhone with the "Network settings" menu still open, enter the correct settings, wait for the carrier to be recognized and show in the status bar, then save them. I have yet to try it, (need to cut down my T-Mobile SIM,) but it would be awesome if it works. My brother's 4s arrives tomorrow, and I'm setting up StraightTalk for him. Will be interesting... Apparently you need to have data before using this method to change the MMS APN, so I'd navigate to that unlockit.nz or whatnot site and download the APN settings to enable data first. (But if I can enter them in the Network settings menu anyway I might as well try to do it without needing to install profiles first.) Will post back to say if it works or not.