I have had Rhapsody for ages. It's good stuff. This is, however, a completely wrong move.
I also have a program called Subsonic. Google it. I can stream *anything* from my home PC to my phone. Despite the best efforts of the music services, there are still vast swaths of music that don't exist on ANY of them. Even then, sometimes, I prefer my own higher quality files, even if the stream is compressed (.ogg) - it's usually higher quality than Rhapsody.
This is simply a BAD move. If I were a T-Mobile customer, I wouldn't be that thrilled.
Rhapsody is a partner now (good move for them, since Sprint has Spotify and At&t has Beats) but free music streaming applies to everyone who participates, not just Rhapsody.
Well now you have the CHOICE to continue using data as you always have, or augment with another "inferior" service which doesn't count. I use Plex for my collection, but I also use spotify, amazon, and pandora. So if those last three are "free" that allows me to repurpose that data for other things. I wouldn't stop using Plex, maybe would use it MORE because my other services now don't count...
Unfortunately where I live, TMO data coverage is fringe, so that is not a realistic option, however the kids phones are on TMO MVNO which are dirt cheap..Voice works just fine.