1. Where in IOS are the APN settings stored? I'm talking about the saved settings file, NOT the user interface to view/edit the settings.

2. And is it possible to "lock" (read only) that file of APN settings? (at my own risk)

I'm working on an unlocked jailbroken iPhone 4 on 6.1.0. The APN settings keep self-modifying backwards (unprovoked) and it disables the phone's functions. The carrier is StraightTalk, and they deny any fault. The initial settings were confirmed correct. The account is in good standing. I've actually used the phone DURING the error. The phone just loses all data connection first, then cell connection, then other services. I'm unaware of any pattern that might be suspect as a trigger.