As Apple apologized for the difficulties experienced by customers seeking to sign up to get one of the hot-selling smartphones, AT&T suspended pre-orders for the new iPhone on June 16.
Apple said it had received 600,000 pre-orders for the iPhone 4, which goes on sale in Britain, France, Germany, Japan and the United States on June 24, "the largest number of pre-orders Apple has ever taken in a single day."
The Cupertino, California, firm said demand 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," Apple said.
"We apologize 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.
AT&T said that pre-order sales were "10-times higher than the first day of pre-ordering for the iPhone 3GS last year" and it was suspending the process.
Apple and AT&T websites were overwhelmed by requests on June 15, the first day of pre-ordering for the iPhone 4, with many customers reporting receiving error messages.
AT&T is the exclusive carrier for the iPhone in the United States.
Apple chief executive Steve Jobs unveiled the new iPhone earlier this month. It features video chat, can shoot and edit high-definition quality video and has a crisper resolution screen.
The iPhone 4 costs $199 for the 16 gigabyte model and $299 for the 32GB version.
The touchscreen smartphone, which comes in black and white versions, will be available in 18 other countries in July and 24 more in August.
Apple has sold more than 50 million iPhones since it launched the touchscreen smartphone in 2007.
Copyright Agence France-Presse, 2010