iPhone app users are a fickle lot.

But they could be highly lucrative, too. A new study by mobile ad firm Greystripe found that users of iPhone applications spend about 9.6 minutes at a time with their apps, accessing them nearly 20 times before they're abandoned.

That exposure could prove lucrative for advertisers and developers who are looking for ways to cash in on the craze behind the iPhone's mobile apps, according to Greystripe. The firm's quarterly Consumer Insights Report (PDF format) looked at how owners of the Apple (NASDAQ: AAPL) iPhone are really using their downloaded apps -- and what the payoff might be.

The study is one of the first to take a close look at users of iPhone apps, the wild success of which just enabled Apple to celebrated its one billionth download. Despite their popularity, however, little has been known of how users interact with the apps they download.

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