The Interwebs are completely berift of any discussion of anyone successfully using a USA T-Mobile SIM.
I got a few Cisco factory-recertified/reconditioned HWIC-3G-GSM's from Blackbox Resale Services (A big thanks to Charlie Wade @ Blackbox for the killer pricing) and gave it a whirl.
Turns out that T-Mobile's HSDPA/UMTS/EDGE/GPRS works perfectly.
For the sake of Google's index'ing on the topic, here's a working config:
Cisco IOS Software, C1900 Software (C1900-UNIVERSALK9-M), Version 15.0(1)M3, RELEASE SOFTWARE (fc2)