I had an old Class 4 Kingston card in my phone and the thing just dragged when transferring music or photos. I finally decided I had enough with Class 4 and went looking for a reliable Class 10 card. This SanDisk does the trick. Now music and photo transfers fly like the wind. I can move over a FLAC album in about 30 seconds to my Droid Razr MAXX with no interruptions like I had on my Class 4 card.