After a harrowing day of problems during the pre-ordering period for the iPhone 4, Apple issued an apology for the frustration many experienced while trying to reserve a copy of the device. The Cupertino based company said that it had underestimated demand and that 600,000 units of the next-generation iPhone were pre-sold, which was the largest total of pre-orders the company had ever had on a single day. The apology was released together with a similar statement from AT&T. The carrier said that the number of iPhone 4 units reserved was 10 times the number of iPhone 3GS models it sold the first day of pre-orders last year. The company added that its web site received 13 million requests to check eligibility for updates, 3 times the previous record for a single day. AT&T also said it suspended sales to make sure there will be enough inventory to fulfill the orders already received and pre-orders will be accepted again if additional inventory can be obtained. Those who ordered the iPhone 4 up until 4:30pm EDT will have their handset shipped on June 24th. Those who got in after 4:30pm EDT will have their order shipped between June 25th and July 5th.