New 4G SIM Card Needed for "4G" Device?

Thinking I may get a HTC Inspire "4G" fairly soon, a SIM card question comes to mind. In order for the new "4G" technology to fully work on this device, will a 4G SIM card be needed for activation? Does AT&T even plan on making that generation of SIM's? I know this new "4G" term isn't truly 100% 4G. It's basically just a more advanced form of 3G, right? If I'm correct, it seems that a new 4G SIM would not be needed in order to use this phone, which is going to be used on prepaid, by the way. My current 3G SIM card would function fine in the HTC, then? Clarification would be greatly appreciated.