I'm having the same problem with my iPhone 5. I spent nearly $800 getting everything all fine and dandy and what do I get? A couple days worth of data before it completely disappeared. I've been without data for a week now. I've called a couple times but customer service is of no help whatsoever. I've updated the APN settings, I did the *22890 steps, I've tried everything I could find.
I think a lot of people are being cheated with this whole plan. I bought two months in advance thinking I'd be golden. Something that nearly every carrier offers shouldn't be such a pain to keep in order. One of the times I called, the person said they weren't equipped to troubleshoot iPhones and had someone call me back. Did ST just go into this completely blind? In any case, if I don't have this problem resolved in the next couple of days, I'm returning the phone.
Also, I'm going to post this five times in a row because of the ridiculous rule they have here. Don't mind me.