What Android phone supports UMA calling? I haven't heard of one yet on any carrier, let alone T-Mobile.
Lack of app availability is a regular part of being an early adopter. Research before buying helps eliminate this disappointment.
As for updated software releases, you don't need a T-Mobile version to install it on your BlackBerry. You can install any version released for the 9900 model no matter what carrier released it. How do I upgrade the OS on my BlackBerry? - BlackBerryFAQ