APN settings keep disappearing I'm on an iPhone 4S, running a fresh install of iOS 6 and I'm encountering a weird problem with my APN settings.

Every now and then, about 2 twice a week, I'll be out and about when suddenly my mobile data stops working. When I check my APN settings (apn, username, password), those fields are empty.
I enter my details and then I'm back online without further issues. 

A couple of days later: same thing happens.
I've tried restoring the iOS, wiping and reinstalling but the issue keeps popping up.

Any suggestions?
I have experienced losing APN settings every iOS version upgrade. That was fixed by using a provisioning profile containing the APN settings. Now the APN settings are maintained during iOS upgrades.

Therefore a workaround in your (though different) situation could be to create a provisioning profile for the APN settings using the iPhone Configuration Utility.

And load that APN provisioning profile to the iPhone.