OK, I'm with T-Mobile in Houston and have a HTC Sensation. From what I know about my phone, I don't think it works HSPA+ service in the 1900 MHz band. Does this mean my phone can't connect on higher speed HSPA+??
I don't believe they are completely turning off 1700 in these markets yet. However, it will happen eventually and it will make phones such as yours totally useless once they are totally switched over and turn off GSM which will most likely be years from now...
Edit: I just realized that there are alot of older phones for T-Mo that only support AWS HSPA. This is a game changer for them in some markets... --
From my post above... 1700 will be dual use (LTE 60-70% & HSPA 30-40%) So those of us with 1700 HSPA only phone will not be thrown back into the dark ages. The difference lies in the max speeds, HSPA phones will top out at 42mbps there will be no upgrade for TMO HSPA to the current max of 84mbps.
How long they will keep it dual use has not yet been released but given there are a lot of older phones that are 1700 hspa only I'd say 5 yrs +/- is a suitable guess more than enough time for customers to upgrade on there own.