This is also a problem with Simple Mobile (a MVNO that I'm trying out with a carrier and development unlocked AT&T Branded HTC Titan). Repeatedly, it will default to T-Mobile or AT&T APN and Cell settings, causing me to lose cell service and internet access. Oddly enough, when they've switched settings and cell/internet is supposedly down, I will get MMS messages. There is no way to set the settings correctly and lock them down from an end user perspective. It's pretty much a wash when it comes to service since there aren't enough T-Mobile towers where I'm at, and after the amount I've already paid for is up, I'm switching to Straight Talk to give them a shot.