There was another thread from a user of an iPhone 4s about this. Seems that T-Mobile moved HSPA+ to the extra 5 MHz they have in the AWS band and re-purposed the PCS band for LTE. AWS was the original band used by T-Mobile for 3G/3.5G service, so in reality they just moved it back where it was. T-Mobile's CTO, Neville Ray, has publicly stated that he wants to get rid of everything but LTE. So, anyone using a non-LTE device, of whatever description, has been notified. "You're living on borrowed time."
I may not like it, myself, but T-Mobile is charging headlong into the 21st century and not stopping to look back.
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