Do I understand correctly that it doesn't play mp3's from the card?
I think you may have to convert the songs to WMA format first.
Which, if so, is kinda BS... screw Microsoft and their propietary music formats. Verizon shouldn't be tryin' to appease them.
1. Use the phone to format the memory card (in Tools > Memory > Card Memory > Options.)
2. Copy the songs into the my_music folder on the card (try to access it directly by memory card reader or USB adapter, not via the phone.) IT CANNOT HANDLE SUBDIRECTORIES! (I think this is what breaks it for most people.) Make sure you just put the files directly into the my_music folder. If it's not there, make sure you did step 1 correctly.
3. The music should show up now. If not, make sure you did not use subdirectories and try to ensure there's not anything overly weird about the mp3 files (i.e. foreign character-only names or whatever.)