NEW YORK, USA: Customers trying to reserve the latest version of the iPhone were thwarted by technical glitches that hindered sales on Tuesday, the first day of pre-orders before the device hits stores on June 24.

AT&T Inc customers reported seeing account information of other subscribers while trying to buy the iPhone4, a spokesman for the firm said. Technical errors also prevented some customers from ordering the device using the websites of Apple Inc and AT&T.

Frustrated by website problems, customers lined up outside some stores to ask AT&T, the exclusive U.S. iPhone provider, to manually process orders.

The problems marked another headache for AT&T, which last week said some iPad users had their personal information exposed via a network security flaw. The Federal Bureau of Investigation (FBI) has opened a probe into the alleged breach.

AT&T spokesman Mark Siegel said the firm had received privacy complaints but it was not clear what information customers had seen because it had not been able to replicate the issue.

"We've received reports of customers inadvertently seeing (other customers') account information during the iPhone 4 purchasing process," Siegel said.

He added customers could not have seen social security numbers, credit card data or call records. He said the company was still investigating.

AT&T said in a statement that people who pre-ordered on Tuesday afternoon would receive their new phones on June 25 or later. It said devices would be available on a first-come, first-serve basis in stores from June 24.

"Because of the incredible interest in iPhone 4, today was the busiest online sales day in AT&T history," the company said in a statement.

An attempt by to pre-order the phone on AT&T's website generated the following error message: "There was a problem with your request. “We're sorry, but we are experiencing a system error that prevents us from completing your request."

Apple's website said the request could not be processed, and it suggested the customer try again later.

Apple did not respond to questions about the website issues that provoked complaints by customers in Los Angeles, San Francisco and New York.

At a Los Angeles AT&T store, customer Bobby Hicks said he decided to try to order in person after failing online. The filmmaker said he had been waiting 35 minutes.

Customers waiting at AT&T stores in San Francisco and New York voiced similar complaints.

In San Francisco, about 20 people waited mid-morning outside an AT&T wireless store and a clerk said the systems had been overwhelmed and were running more slowly than usual.

Kevin Wong, a systems engineer waiting at the San Francisco store, said he had been in line for about 20 minutes after he was unable to buy the device online.

"It bothers me, but what can you do? You've got to wait in line. It's better than the DMV," he said referring to the state's Department of Motor Vehicles, which is notorious for long wait times.

The new iPhone starts at $199 and is slimmer than the current handset. It boasts a higher quality screen and better battery life. It will allow video chat via Wi-Fi for the first time and has a gyroscope sensor for improved gaming.

Brian Marshall, an analyst for Gleacher & Co, formerly known as Broadpoint Amtech, said the online overload may be partly due to consumers becoming smarter about ordering online rather than camping out for hours or days at stores to buy iPhone.

"People are a little bit wiser about efficient use of time," he said.

Apple shares rose $5.41 at $259.69 on the Nasdaq. AT&T shares rose 37 cents at $25.54 on New York Stock Exchange.