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Apple said in a press release that the total was "far higher than we anticipated, resulting in many order and approval system malfunctions. Many customers were turned away or abandoned the process in frustration."
The company continued, "We apologize to everyone who encountered difficulties, and hope that they will try again or visit an Apple store or carrier store once the iPhone 4 is in stock."
iPhone 4 preorders through Apple that could not be placed on Tuesday will have to wait, as Apple has said new orders will ship by July 2, more than a week after the June. 24 launch date.
Those who didn't get their order in on Tuesday in the U.S. may have to wait even longer, as AT&T also announced Wednesday that it has suspended preorders following unprecedented demand for Apple's latest handset. The exclusive carrier of the iPhone in the U.S. said that demand was ten times greater than that for the iPhone 3GS in 2009.
Both Apple and AT&T experienced problems as the companies began accepting preorders on Tuesday. AT&T's systems were unable to verify eligibility for some existing customers, while Apple was forced to turn down callers to its 800 number.
The iPhone 4 is set to launch next Thursday, June 24. In addition to the AT&T network in the U.S., the phone will debut with multiple carrier partners in France, Germany, the U.K. and Japan. Apple has announced that the iPhone 4 international launch will ramp up to 87 total countries by September, its fastest-ever global deployment of a new handset.
The 600,000 preorders taken Tuesday suggest that Apple is on pace to blow out its previous sales records with the iPhone 3GS. Last year, Apple sold over a million of the device in its first three days.