It usually goes by the euphemism "traffic shaping." Cox started doing that a few years ago, and when their customer support lied to me about it I immediately switched to DSL and never looked back. And they *did* lie, because it came out just recently during congressional hearings that they'd been doing it for a while, which confirmed what I and some other users had figured out at the time.
AT&T claims publicly that they have no problem at all with BT and other filesharing as long as the files are legit, and indeed, so far, I've never had the slightest problem with them and BT. I still strongly dislike the company for other reasons, but as far as this goes they seem to be doing the right thing.