Apple and AT&T took 600,000 pre-orders for the iPhone 4 in its first day of sales in the US, a market with a population six times that of Korea.
The success of the launch could cause more problems for Apple's already strained supply chain. Supply for Apple's mobile devices is not expected to balance with demand until October, research firm Asymco has warned.
The strained supply impacted Apple's launch sales for the iPhone 4, which could have been as high as 2.5 million - compared to 1.7 million - without the limitation, according to a Kaufman Bros analyst.
But one constraint, the limited availability of display panels, is reportedly beginning to lift.
Analyst firm Susquehanna has raised its iPhone production forecast by over 4 million units as a result of healthier supply for iPhone displays, Street Insider said.
The firm lifted its sales forecasts for the iPhone line in the fourth quarter to 11.6 million, a 39% sequential increase.
KT's shares on the NYSE rose 2.6% in after-hours trading. Apple's Nasdaq stock is up $1.10 to $253.07.
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