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.
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.