Having lots of music downloaded is a great way to not only enjoy what you want, ssg978, but also avoid any extra data used from music streaming. My brother does the same thing with his phone. It's possible that your phone isn't able to find the music files since they aren't saved in a place where it will look.
If you access the storage menu on your phone, does it recognize the SD card? You might need to format the memory card through the phone itself: http://vz.to/1LiyZQV . After that, download a music file through the phone itself, like through Amazon Music or any other music service you might have. Just be sure to use WiFi for any downloads. This will put a music file folder on your phone, which you can then add additional music from your computer in to it.
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