Heh, heh. Saw this one coming a mile away. With the DRM update in iTunes, iTunes phones won't play newly purchased DRMd music.
Digital rights management means that whatever plays the content (music, video) must be updated every time the DRM is updated -- and the latter occurs every time a weakness is discovered in the DRM mechanism. Such weaknesses are inevitable (some are driven simply by faster hacking hardware), so updates will occcur every few years.
So every few years all the hardware that works with the DRMd media must be updated. That takes time and money, and sometimes it just won't work. The hardware is obsolete. It works best if the owner of the DRM also owns the hardware.
So if your phone is going to play Microsoft's DRMd music, it needs probably be a Microsoft phone. If it plays Apple's FairPlay DRMd music (btw: AAC is the format, NOT the DRM, AAC is not an Apple product) it better be an Apple phone.
Interesting how these things work.