Apple has apologised for yesterday's iPhone 4 ordering mess in the US, and boasted that it and its carrier partners had taken more then 600,000 orders for the new smartphone.

Meanwhile, AT&T confirmed that is has suspended pre-orders through its site and stores.

"We apologise to everyone who encountered difficulties, and hope that they will try again or visit an Apple or carrier store once the iPhone 4 is in stock," Apple said in a statement released Wednesday, referring to the ordering bungles that left many users frustrated and angry.

Apple added that demand for the iPhone 4 was "far higher than we anticipated," which resulted in "many order and approval system malfunctions."

Apple's and AT&T's Web sites essentially collapsed under the load, returning errors and time-outs when many customers tried to place orders. By the end of the day, both Apple and AT&T had exhausted the supplies they'd set aside for delivery on 24 June, the official iPhone 4 launch date.

"It was extremely frustrating," said Brian Marshall, a Wall Street analyst with BroadPoint AmTech. "I continue to be extremely frustrated with AT&T and its service." Marshall said he had tried 10 or more times Tuesday to order an iPhone 4, all unsuccessful.

"That's par for the course for AT&T, unfortunately," said Marshall.

For its part, AT&T said that sales were 10 times higher than the first day of iPhone 3GS pre-ordering in June 2009, and added that it had received more than 13 million upgrade eligibility requests during the day, a number three times higher than the record.

"Given this unprecedented demand and our current expectations for our iPhone 4 inventory levels when the device is available June 24, we're suspending pre-ordering today in order to fulfill the orders we've already received," AT&T spokesman Mark Siegel said in an e-mail Wednesday.

AT&T has removed the iPhone 4 from its website. Currently, only last year's iPhone 3GS can be found there.

Siegel did not set a date when AT&T would again take iPhone 4 orders. "The availability of additional inventory will determine if we can resume taking pre-orders," he said.

Apple, however, still shows the iPhone 4 16GB and 32GB models as available on its online store, with a projected ship date of 2 July.

Unlike Apple, AT&T's statement did not mention customers' encounters with its ordering system, or apologise for the problems.

Some customers had to go to great lengths to make sure their orders were processed as promised. Computerworld reader Dennis Hoffman, for example, placed his iPhone 4 pre-order with AT&T between 4am and 4:30am ET Tuesday, just hours after the carrier started taking orders. Later in the day, however, Hoffman received an email that said his order had been canceled.

Hoffman spent hours Tuesday night working his way through AT&T's online chat and telephone customer service, but was eventually rewarded when an AT&T representative restored his order and said he would receive it on 24 June.

Marshall has projected iPhone sales during 2010 at 40 million units, a 59% increase over 2009, with 8.8 million of those selling in the quarter that ends June 30, a jump of 68% over the same period last year. "These are very conservative," he said. "I have a high degree of confidence that Apple will exceed those numbers."

Apple, AT&T, Best Buy, Radio Shack and Wal-Mart are slated to kick off in-store sales on June 24.

AT&T is telling iPhone 4 buyers that pre-orders have been "temporarily suspended".