The answer to your first question is "no." That PPC-6700 will ONLY work with Verizon...Verizon and Sprint will only activate phones on their service that they sell to their customers, so no taking a Verizon phone and using it on Sprint, for example.
As to your second question...if you're liberal about your data usage and use it a lot, then it might get their attention. A lot of people never have a problem though.
If you're absolutely intent on getting something with a QWERTY keyboard, your options are very limited, as all carriers consider anything with a QWERTY keyboard to be a PDA (except for Verizon's enV and u740...and no, you don't want either one).
Given your requirements, you are basically limited to a Motorola Q from Sprint...you can still order it with the standard $15 PowerVision unlimited internet plan.
However, Sprint's customer service sucks giant slimy toad droppings. I'd highly recommend avoiding them, especially if they don't have EVDO service in your area (if they don't, then the internet will actually be 1xRTT, which is typically slower than EDGE on T-Mobile).
If you can get away from requiring a QWERTY keyboard, then the Nokia N75 from AT&T becomes a very viable option, as unlimited internet for it is $20 (and comes with 200 SMS/MMS/IM messages) because it's not considered a PDA. If you really REALLY want a QWERTY, you can buy an add-on folding Bluetooth keyboard for around $100, and the phone is $50 from a lot of AT&T online dealers. Even if AT&T doesn't have 3G in your area, EDGE will be faster than your old T-Mobile service.
Oh, one other thing. Most carriers won't even admit to 2 year contracts existing anymore. You might be able to find one, but the phone will be more expensive.