I had spotify on my windows phone a while ago. The two problems were that there was no specific list for offline songs, and the major one being that the offline playlists were stored on the internal storage meaning I could only have 10-20 albums at a time. all the while I had an 30gb sd card plugged in and completely empty, even though I set all music and photos to be stored on the SD card in the settings menu.
That was early this year before windows phone 8.1 came out.
I'm thinking of signing up again (because the windows music app is freaking terrible, as well as other other music service). I just want to know before I do, will the offline playlists be stored on the sd card or the internal memory