Apple has announced that it has received more than 600,000 pre-orders for the new iPhone 4 - far higher than it expected to receive.

This is the largest number of pre-orders Apple has ever taken in a single day, resulting in many order and approval system malfunctions. Apple said many customers have been turned away or abandoned the process in frustration.

"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.

There were reports in the US on Tuesday that, when some AT&T customers logged into the mobile operator's site to pre-order, they inadvertently gained access to different users' accounts. AT&T issued a statement yesterday acknowledging that it had received privacy complaints about the incidents, but could not replicate the issue.

Since Apple's initial stock of iPhone 4s have been accounted for with in-store reservations or home delivery, Apple's shipping dates for orders placed now have been pushed back to "by July 2". Customers can no longer reserve a phone for in-store pickup on launch day, though Apple stores will have a limited supply of iPhone 4s on hand for walk-up customers.

The news comes as Tesco Mobile announced it will also stock the iPhone 4 in the UK. Tesco is over a week behind O2, Orange, T-Mobile, Vodafone and 3 in announcing it will stock the handset. The 16GB iPhone costs £499, while the 32GB handset is priced at £599.

Apple's latest smartphone was unveiled by Steve Jobs last week at the company's Worldwide Developers Conference (WWDC).

See also: O2 unveils iPhone 4 early upgrade offer

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