The company stopped taking advance orders just one day after orders started, citing inventory issues and unexpectedly high demand.
In a statement, AT&T said it is suspending the orders "in order to fulfill the orders we've already received."
Apple Inc. said Wednesday that it and its phone company partners took orders for more than 600,000 iPhone 4s in one day, the highest number it's ever seen, despite widespread problems getting orders through overwhelmed computer systems.
The crush of orders sets the scene for long lines and potential chaos at stores when the phone is released on June 24.
Apple and its partners started taking orders for the iPhone 4 on Tuesday. On Wednesday morning, AT&T Inc., the exclusive carrier in the U.S., had stopped taking orders, saying it had to focus on fulfilling orders already received.
At midday Wednesday, Apple was accepting orders only for black models, and would only guarantee shipment by July 2. The white model was unavailable for pre-order.
Dallas-based AT&T said it received ten times as many pre-launch orders on the first day for the new iPhone model as it did for the previous model last year.
AT&T also said it logged more than 13 million visits to a Web page where current customers can check if they're eligible for a subsidized upgrade to the new phone. That number was three times higher than the previous record for upgrade checks.
The price of the phone starts at $199. Customers who aren't eligible for upgrades will pay $200 more.
Last year, Apple sold more than a million units of the new model, the 3GS, in the first three days. It was the most successful debut for a smart phone yet, and Apple struggled to keep it in stock for months.
The iPhone 4 will feature a higher-resolution screen, longer battery life, dual cameras and a thinner design than last year's model. The suspension of orders comes a day Apple and AT&T faced two major problems taking orders for the newest iPhone: Buyers reported problems registering their orders and an apparent glitch in AT&T's website was steering some customers into strangers' accounts.
Troubles in meeting demand for the iPhone aren't new.
But the latest apparent breach and other recent security foul-ups by AT&T could lead to identity theft - and have consequences for both companies. Customers have called for Apple to allow other carriers to serve the iPhone in the U.S., and the latest problems offer another argument.
The computer systems at Apple Inc., maker of the iPhone, or AT&T Inc., its exclusive U.S. carrier, have had various problems every year since the first iPhone launched in 2007.
Some customers who tried to buy an iPhone 4 on Tuesday said they were met with error messages on the company websites, and lines formed in stores as clerks tried to get orders into their systems.
On Gizmodo.com, a technology website, several readers posted stories of trying to log into their AT&T accounts to upgrade to the newest iPhone and being sent instead into strangers' accounts. That could set the stage for identity theft scams such as ordering other products under that person's name.
AT&T said it received reports of customers seeing the wrong account information but wasn't able to replicate the problem and was investigating. But the company said the personal information users were seeing in one another's accounts didn't include Social Security numbers, credit card information or detailed call logs.
Just last week, AT&T plugged an embarrassing security hole on its website that exposed the e-mail addresses of people who had bought another new Apple product, the iPad.
And in January, AT&T acknowledged to The Associated Press that a problem in its network was causing some wireless customers to land in strangers' Facebook accounts when they tried to check their own accounts using their smart phones. AT&T said it was fixing that glitch.
It doesn't happen often, but the Internet can forget who is who when multiple people log onto a site at the same time.
AT&T blamed a "misdirected cookie" for at least one of the problems in January. A cookie is a file websites place on users' computers to identify them. If the Internet provider fumbles a cookie and sends it to the wrong computer, the person using that computer will see a Web page he or she wasn't expecting.
Apple representatives didn't immediately respond to requests for comment late Tuesday.
Associated Press Writers Tomoko A. Hosaka contributed from Tokyo. Svensson reported from New York.