No wonder AT&T is throttling you...
If you want your phone to act as a "hot spot," then set it up to do exactly that. Otherwise, I think you're an idiot for complaining that they're giving you a hard time about mobile data usage. It's a phone, not a personal computer.
You can change providers, but anymore I think you'll find just about any carrier will eventually be throttling you by some margin. If not now, they will be shortly since that always seems to be the trend once one company begins that movement.