For HSPA+ IIRC tmobile is mostly 1700, with some cities converted their older 1900 network to HSPA+. ATT is mostly 1900 for HSPA+
AT&T runs HSPA on 850 and 1900. I'm not sure how they handle areas with overlapping frequencies, but I'd imagine they still rolled out HSPA on both bands in the same area. There's be no reason not to.
TMobile is HSPA on AWS, which is 1700/2100. AT&T also own some AWS licenses they were planning to use for LTE, but I don't believe they've rolled any out since the TMobile purchase fell through. I think they only own it in about a dozen metro areas.