Buying the popular Apple Inc iPhone has become more difficult for residents of the Big Apple.

Consumers with Manhattan postal zip codes who attempted to purchase an iPhone through AT&T's website on Monday were told that the product was unavailable, according to a report on Reuters received the same response when logging on with a New York zip code.

A representative of AT&T, the exclusive U.S. provider of the iPhone, said in an email that the company periodically modifies its promotions and distribution channels. The iPhone is available in our New York retail stores and those of our partners.

Sales representatives at Apple retail stores in Manhattan, reached by phone on Monday, said that the iPhone was available, and an Apple corporate spokesman was not immediately available for comment.

IPhone owners, who have some of the biggest appetites for mobile Internet use, in particular have criticized AT&T's wireless network as being too slow.

Craig Mathias, a principal at wireless consulting firm Farpoint Group, said that all network carriers are struggling to cope with the rising popularity of wireless data services, which require more network capacity than standard voice calls.

He speculated that AT&T may be trying to ease congestion on its network in the wake of the holidays, when many consumers who received iPhones as gifts would start using the devices at the same time.

Apple's iPhone, a cell phone with computer-like capabilities such as Web browsing and video games, has become one of the most popular smartphones on the market.

We're expecting our handsets now to do everything we do while in the office or at home, said Mathias.

As the initial burst of post-holiday activity levels off, Mathias predicted that AT&T would make more phones available once again.

If they're seriously out of gas and can't service any customers in that area, that is a major problem, he said.