Customers attempting to reserve the next iPhone were thwarted by error messages on the websites of Apple Inc and AT&T Inc on Tuesday, the first day of pre-orders for the phone.
AT&T, the iPhone's exclusive operator, declined to comment, and Apple did not immediately respond to a questions about the technical problems that provoked complaints by customers in several cities across the United States, including Los Angeles, San Francisco and New York.
Customers lined up outside some stores to ask AT&T employees to manually process their orders.
One attempt by a Reuters reporter to pre-order the phone on both Apple and AT&T's websites generated error messages. The following came from AT&T's website.
There was a problem with your request, it read. 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.
Bobby Hicks, a customer at a Los Angeles AT&T store, said he had been unable to order online and so was trying to place an order in person.
The film maker said he had been waiting 35 minutes.
Customers waiting at AT&T stores in San Francisco and New York voiced similar complaints.
At an AT&T wireless store in downtown San Francisco, about 20 people waited in a line that stretched outside the store by mid-morning.
It appeared that orders were being processed at the store, but an AT&T 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 Department of Motor Vehicles, which is notorious for long wait times.
Earlier this month Apple unveiled the iPhone 4, which will go on sale in Apple and AT&T stores on June 24. Pre-ordering began on Tuesday.
The redesigned iPhone starts at $199, and is a quarter slimmer than the current handset and boasts a higher quality screen and better battery life.
It will also allow video chat via Wi-Fi for the first time and has a gyroscope sensor for improved gaming.
Apple shares were up $4.55 at $258.83 on the Nasdaq. AT&T shares were up 27 cents at $25.45 on New York Stock Exchange.
(Additional reporting by Caroline Madrid in Los Angeles and Paul Thomasch in New York; Editing by Steve Orlofsky)