The Netshare app by Nullriver is based on SOCKS -- an Internet protocol that enables client-server applications to transparently employ the services of a network firewall. Netshare essentially converts any iPhone into a portable Wi-Fi hotspot, with all Wi-Fi-enabled devices able to share a broadband Internet connection wherever a cellular signal is available.

"We're trying to get ahold of Apple right now," said Nullriver spokesperson Maksim Rogov in an e-mail. "Until we hear from Apple, it's hard to say what the real reason is, because if it was AT&T, well, AT&T is not the iPhone service provider outside the U.S."

Not On AT&T's List

Wireless carriers are understandably not happy about programs such as Netshare because they allow users to bypass their cellular networks and avoid data-access fees.

"The iPhone is not intended to be used as a tethering device and we have no plans to offer separate tethering plans for it," said AT&T spokesperson Wes Warnock. "We offer LaptopConnect cards that you can use to access our wireless data network. Those cards offer typical download speeds as high as 1.7 Mbps."

Warnock noted that AT&T wireless provides tethered access for a monthly fee on smartphones from LG, Motorola, Nokia, RIM, Samsung and others, but the iPhone is not on the carrier's list of supported devices. "For customers looking for a smartphone with tethering capability, we have many other options," Warnock said.

Developer Mystified

Some media outlets were quick to suggest that Nullriver had come under pressure when its Netshare product description was cleared from the Web site earlier today. But Nullriver says it is as mystified as everyone else as to why its application was pulled.

Nullriver says it is currently trying to get Netshare back on the App Store.

"Sorry to all the folks that couldn't get it in time," Rogov said. "We're hoping we'll get some feedback from Apple tomorrow. At the very least, I would hope Apple will allow it in countries where the provider does permit tethering."

The fact that Netshare made even a brief appearance on the App Store surprised industry observers. To keep IT administrators from worrying about rogue applications ending up on iPhones in enterprise environments, Apple had promised to thoroughly vet the applications it offers before making them available for download.

Given its recent woes with its MobileMe subscription service, Apple has once again raised questions about how prepared it is to successfully market the iPhone worldwide. Apple did not immediately respond to a request for further information .