) -- Manufacturing issues have forced


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to push back availability of its white iPhone 4, just a day before the black version of the new iPhone is due to hit store shelves.

"White models of Apple's new iPhone 4 have proven more challenging to manufacture than expected, and as a result they will not be available until the second half of July," Apple said on its Web site. "The availability of the more-popular iPhone 4 black models is not affected."

Last week there were signs that something wasn't quite right when neither Apple nor partner


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taking pre-orders for the white iPhone 4.

Both Apple and AT&T have

struggled to cope with the volume of iPhone pre-orders

, prompting Apple to take the unusual step of apologizing to its customers. In a statement released last Wednesday, Apple explained that it had taken more than 600,000 pre-orders for the new iPhone 4, along with AT&T. This, it said, was the largest number of pre-orders it had ever taken in a single day and far higher than anticipated.

During Apple's recent second-quarter results, iPhone shipments climbed a massive 131% compared to the same period last year, reaching 8.75 million devices. iPhone revenue also rose dramatically, reaching $5.45 billion, compared to $2.43 billion in prior year's quarter. iPhone sales now account for around 40% of Apple's total revenue.

At market close on Wednesday, Apple shares had hit $270.97.

-- Reported by James Rogers in New York

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