That's interesting. I haven't seen any T-Mobile 8700s yet. If you're looking for an upgrade to the latest and greatest, this is a good upgrade.
T-Mobile usually has a $75-$100 out-of-warranty repair charge on most BlackBerries.
If you want to keep your accessories, etc. I would look at the 7290--it has enough memory to run the latest operating system and a much better backlight.