T-Mobile includes the personal hotspot at no extra charge. I just switched from AT&T too and have been really happy so far. My phone only gets Edge speeds right now, only because they haven't "reframed" their cell towers yet. (not exactly sure what that entails, but I understood it to mean that after reframing my phone would be on 4G, have better reception, etc.)
Basically they currently have GSM on the 1900MHz band and HSPA+ on the AWS bands (1700/2100). They're in the process of reducing the capacity allocated to GSM, splitting HSPA+ onto all the frequency ranges, and adding limited LTE on the AWS bands. Later on they're going to reduce the GSM capacity a bit further while expanding the LTE capacity on the AWS bands. There's a nice little chart that shows this much better than I described it, while continuing to gloss over any technical details.
