Thank you for confirming that. For some reason Apple does not list the micro-simcard slot on the tech specs page of the iPhone4. Why would that be?
Because it is not useful for anything aside from its use with the network carriers... You change the sim cards when you change carriers. In Europe, and other countries where there are multiple carriers, it is useful... because an unlocked iPhone can use multiple simcards to change between carriers. In the US, where there is only one official carrier, that's not useful.