Do not upgrade your plan. T-Mobile does NOT have seperate 4G plans. it is the same 3.5G network that they have had all year just with the 4G marketing attached. If you are not getting HSPA+ speeds, that simply means that the tower near you has not been upgraded even though your city is a HSPA+ enabled city. I live in the atlanta area and I get 8Mbps in some areas while in other areas I only get 1Mbps. I have the $5.99 Tzones and have been doing speed tests since Feb 2010.

If you change plans, you will just end up paying more to access the same network towers and service.