Wondering what goes into the process of determining what iPhone applications make the grade for Apple's App Store? You're not alone--the developers who write those programs sometimes find themselves wondering the same thing.

Apple's online store for iPhone apps has been a success by many measures--the company says it recorded 10 million application downloads during the first weekend after its July 10 opening--but some kinks still need to be worked out of the system. Developers have already expressed frustration over how long it takes application updates to appear on the App Store. Now they're puzzled by why Apple decides to approve some applications for the store and remove others, often with little warning.

When Steve Jobs unveiled plans for the App Store in March, he noted that there would be limitations on what kinds of apps would gain Apple's approval. The company specifically cited porn, privacy-breaching tools, bandwidth-hogging apps, and anything illegal, though Jobs' presentation also included a category called "unforeseen." It's the nebulousness of that category--and what developers feel is a lack of communication on Apple's part--that's causing a lot of confusion among a growing number of software makers.

"Apple needs to do a lot of work to improve communications between developers and the people in charge of the App Store," said John Casasanta, president of Tap Tap Tap. "In my experience, communication has been pretty spotty so far, as opposed to the great service Apple's provided with Developer Technical Support. We have questions that have gone unanswered so far and unlike DTS, we don't even have any kind of direct contact with anyone there, unfortunately."

Consider the case of Nullriver's NetShare, an application that allows you to tether your computer to the iPhone to share the 3G connection. The US$10 application was received with some excitement from iPhone users even though AT&T said it wouldn't allow data connections to be used in this way.

Last Friday, NetShare disappeared from the App Store, with developer Nullriver in the dark as to the reasons why. "NetShare did not violate any of the Developer or App Store agreements," the company wrote in a note posted to its Web site last week. "We're hoping we'll get some feedback from Apple today."

NetShare reappeared on the App Store later that day--only to disappear again soon after.

On Wednesday, Nullriver said that it finally made contact with Apple, blaming the earlier lack of communication on "automated e-mail systems being employed on both ends, which resulted in e-mails being lost in transit." The company says its working with Apple to return NetShare to the App Store.

Still, other developers that spoke with Macworld said lack of communication is a common occurrence when the App Store is involved.

"It's like the App Store division is this top secret, untouchable branch of Apple," said Casasanta.

Also last week, movie lookup application Box Office joined NetShare as an app that got removed from the App Store. In a posting at MacRumors.com, Box Office developer Cyrus Najmabadi said he had no idea why the app was removed.

"Apple pulled the app [July 31] without giving my any notification that they were doing it, or what their justification was for removing it," said Najmabadi. "I've tried to contact them about the issue, but it's been a complete dead end."

It's not just applications that get removed from the App Store that can cause developers to scratch their heads--the approval process can also be confusing, based on some of the programs that have made the grade.

The $1000 I Am Rich application slipped through Apple's vetting process.

Take as an example an application called I Am Rich. The app, listed