Believe it or not, T-Mobile actually doesn't discourage customers from using unlocked devices. T-Mobile recently redesigned and changed the link for the configuration (dotac) tool. It appears to be completely internal to the company now and not publicly available.
Thanks for the info about the internal tool.
In my opinion, taking down the public site and requiring people to now call customer care in order to get the phone programmed does discourage people from using unlocked devices. Not only do you have to wait on hold, and go through the phone screening system, but some customers care agents may not be well trained in how to use the tool, especially with phones that T-Mobile has never carried.
Whatever they may have been paying wdsglobal to host the site, it's probably well worth it. People had a tool they could use on their own and not have to clog up the lines with needless requests. But nonetheless, if that's the way T wants to do it, I'll advise people to call customer care now when they get a new unlocked device.