I don't see how they are "treating" data from Rhapsody different than how they are treating data from XBox Music or Beats differently when examined at the network level. This promotion is at the accounting level only. When the two become intertwined like Netflix/Verizon/Level 3 peering drama then I agree with you. But unless somebody can demonstrate T-Mobile degrading the quality of the network traffic for non-Rhapsody streamers I don't think this has anything to do with net neutrality.

There is a line between marketing/cross promotions business relationships and encroachment on net neutrality, consumers need to be vigilant, but the line does exist.

They are treating Rhapsody data different from Hacker News data. Or data from my personal blog. That they are consistent among their partners is irrelevant.