You keep your current data plan and dont be surprise when the other carriers follow suit since most are planning on going 4g around 2011 and 2012. Having 20 million customer downloading with no limits really puts a strain on the network.The start of 2011 att will be boosting our 3g speeds up to 7.2mps, so when we go to 4g there will not be too big of a drop if you go from 4g back down to 3g

Just make sure you don't ever let your unlimited plan get replaced either online, over the phone or in the store. Its a pain to get it back on if there is a mistake where it was taken off, has to get higher up approval to get the unlimited plan back on.