I switched from a TouchPro 2 to the Amaze this week and now I can't tether my phone to my computer to share the internet connection. This worked on my old phone and the one before that. It was a feature that I didn't use that much but was handy at times.
When I called T-Mobile they told me that I previously was accessing the tethering for free as it was an "un paid and unsupported feature that happens to have worked on your phone." Now that they are "supporting" it they tell me they have to charge for it and will stop it from functioning on older phones too... unless you pay $14.99 per month. The same applies if you want to use the phone as a wifi hub. I have no idea how long this feature would have kept working on my old phone.
None of this was explained to me when I extended my service 2 years and I am not happy about this change.