I want to pickup a couple MicroSD cards for Christmas for my wife and daughter. They both have the LG Optimus S (which is an awesome phone by the way if anyone is considering it). Wanted a 16GB for the wife and an 8GB for my kid. The question is, I see Newegg has them relatively cheap. $15-$20 for the 8GB and $25-$30 for the 16GB. But they talk about Class 2 and Class 4 all the way up to Class 10 or something. How do I know which I need to buy for their phones?