AT&T doesn't stay better, they also canceled some pre-orders, saying that they had ten times more pre-orders on the first day compared to the 3GS. I don't know what's with these cancels, but it is certain that this will put some people in an unpleasant situation, especially those who wanted to have their phone on the first day of shipping (OK, who didn't want?). Considering this enormous demand for the iPhone 4, pre-orders which are made today are going to be delivered much later.
By the way, Apple has already started shipping iPhone 4 for those who ordered it in the first period of pre-orders. They will most probably be received on the 23rd of June.