I recently switched from the Bold 9000 to the Torch. When I loaded my old micro SD card into the Torch, I was able to access my pics and videos but not my music. My music was originally downloaded via AT&T/Rhapsody.
You'll have to take this up with AT&T and Rhapsody. What you downloaded weren't real (portable, non-drm) MP3's, but rather an encrypted file type that was locked to your previous phone. In a nutshell, you didn't purchase the songs, you only purchased a license to listen to those songs on the phone they were originally downloaded to.
