I bought a 64 sandisk sdxc class 10 and tried it in the phone. Didn't work. Formatted to fat32 with a partition program, still wouldn't work. Got fed up, deleted all the partitions, threw it in the phone and itr was recognized, but blank. Had the phone format it, and it works. Phenomenally actually. Haven't tested read/write, but I've filled it a few times over looking for problems and had none. Without looking I think I have just shy of 40 used on it right now.