Okay folks let me break it down for you.
If you call in too much or get reported as a verbally abusive caller you will get routed to the "Bronze Queue" which is where you sit on hold for an eternity and if you are really lucky you will get a rep after sitting in the penalty box forever.
Anyone who knows anything about IVRs knows you can be routed to any particular queue based on a variety of factors. For example when I worked for a computer company your call would be routed based on your phone number, zip code, call history, buying history, etc. So if you live in the Bronx you would most likely get an outsourced rep if you called from home. But let's say you work in Manhattan and call from work. You would most likely get routed to a seasoned veteran rep in a special queue in the U.S. because the system figures a caller from Manhattan is potentially a bigger spender.
At T-Mobile there are about 20 call centers (give or take) in the U.S.
To my knowledge and to the best of my memory, the only departments that are outsourced are Activations, FlexPay (unless the queue is backed up then you might get an American), Prepaid (Monthly 4G), Migrations (Employee Discount Program), Puerto Rico customers (for obvious reasons), Some NTC calls (for porting issues), and PrePaid/FlexPay tech support.
If you have good ol' PostPaid service you should be getting someone in the U.S. Keep in mind it is still possible to get someone in the U.S with a foreign accent. Doesn't mean they are an outsourcer.
I hope this clears up a few things.