In March, when Apple opened the iPhone up to third-party applications, it yielded little control over the popular gadgets: iPhone applications are subject to Apple’s approval and can be downloaded only from Apple’s Internet-based App Store.

Now, developers are complaining about what they see as Apple’s capricious rejection of promising apps. Some have been turned down because they “duplicated the functionality” of proprietary Apple applications, even though the same is true of notepad apps, stock tickers, and the like available through the App Store. A program from the German developer Dirk Holtwick, which let Web applications access the iPhone’s hardware, was rejected for being “of limited utility,” while apps like iBeer (left) were deemed useful enough.

“It’s almost like a nightclub, and we’re uncertain how we get past the bouncer,” says Brit Gardner of the Dallas development company Figaro Interactive. And, many developers argue, that uncertainty stifles innovation. “If you spend a lot of time and a lot of money developing an application, and in the end it’s not accepted by Apple, and you don’t know why, that’s an investment that’s worthless,” says Holtwick. “So you think twice about creating an application.”