I upgraded my Instinct to a 8GB SDmicro card and downloaded all my music to the phone with no problem.  However I then found that whenever I attempted to play them I would get an error message "too many songs, delete some and try again".  I tried several times with Sprint support to get an answer since I was only using 40% of the card's memory.   I finally found a user forum on the sprint site and found that others had the same problem.  The actual problem is that the player for whatever reason cannot handle WMA files.  After I converted my files to MP3 format the problem went away.