Users trying to order the iPhone on Apple’s website received an error message: “Your request couldn’t be processed. We’re sorry, but there was an error processing your request. Please try again later.” Attempts to preorder from AT&T’s website yielded similar error messages.

Calls to AT&T’s customer service line returned a pre-recorded message saying that the company was facing extremely heavy call volumes. A new Apple app, launched Tuesday morning, that allows existing Apple customers to use their iPhone or iPod to pre-order the iPhone 4 was offline by mid-afternoon. Twitter, recovering from its own crashes earlier in the day, lit up with accounts from frustrated iPhone shoppers.

Even AT&T’s retail stores were unable to order new iPhones for customers. The computer system at an AT&T store near Manhattan’s Grand Central Station remained crashed late Thursday afternoon, forcing workers to take orders manually on paper. More than two dozen shoppers were queued up, waiting for their turn to order.