I have a SanDisk 32GB Class 2 card in my phone and it is very fast, tests like a Class 4, everything opens quickly, movies play perfectly, no corruption etc... Got it on Amazon 9 months ago for $60, I'm sure they are cheaper now. The point is, you get what you pay for. I chose to pay more and have much less of a chance of all my pictures up and vanishing or my data becoming corrupted or my MD5 checksums not validating etc...
You do not NEED a class 10 holy omfballs card in your smartphone, a good class 2 is going to be just as good and even if there is a somewhat appreciable difference in testing, I highly doubt you notice it in every day actual operation of your device.
-Bionic Eclipse Rom, 64gb microsd, extended battery, winning
-D3 MavRom, wireless tether hack, unlocked globally
-DX Liberty V3 2.0 1.35GHZ low voltage, backup phone
-boost mobile Epic 4G 1.4GHZ Marcusant R.I.P.