This is what comes in an email sent by Apple recently 
Dear Customer, we were unable to complete the authorization process for your iPhone order. As a result, we had to cancel your iPhone order. To complete the purchase of your iPhone, please visit an Apple Retail Store or an AT&T company owned retail store. We apologize for this inconvenience.
What do you think has it to do with the iPhone4 , is it the system slip by AT&T or the shortage of displays for iPhone 4 ? There’s no more news on this all we’ve seen are the comments of frustrated folks who wished they had a better fortune with their pre-orders .
So this means iPhone developers need to wait few more days to sell their apps to the iOS 4 ready platform users .
