Let the hive mind of Engadget get that for you.
"I just switched to Sprint from Verizon about three months ago for the Pre. Then I went for the Hero about a week ago. Now, I miss my hardware keyboard and am thinking about switching to the Moment. I am still able to switch back to Verizon if I want and get the Droid when it arrives. Should I just trade up to the Moment when it comes out, see if I like it, and if not switch to the Droid? Or something else entirely? Help!"
Prior art is a patent thing, not a trademark thing. If you apply for a trademark for a product/service in a particular region before someone else does, and it's in your name, you get to use it. They don't. T-Mobile didn't apply for the trademark in Canada, so Telus wins. I would guess that Telus could actually file a countersuit against T-Mobile for the arrogant thinking that it can boss around someone over the use of their own trademark.