Developers of programmes for the iPhone have already managed to make a decent living

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selling hundreds of thousands of copies of games from their living rooms or garages.

But now, a new way to profit from writing software for the iPhone is emerging: Sell the apps, then sell your company.

With the number of downloads through Apple’s App Store topping one billion and more than 40 million iPhones and iPod Touches sold since 2007, an increasing number of companies are seeing the mobile industry as a source of sustained revenue. Only recently, IAC-Inter-ActiveCorp, the internet media conglomerate founded by Barry Diller, and Amazon.com, have bought app developers. Smaller companies have begun to assemble properties.

Since Apple showed that new apps sell phones, the market for apps is expanding quickly. Palm, Research in Motion, Nokia and Microsoft are all building app stores to work with phones running their operating systems. Apps can also be built for phones running Google’s Android software.

Most of the action is still in iPhone apps, which is what makes Apple’s Worldwide Developer’s Conference this week in San Francisco of interest to developers and potential investors.

Developers will be showing new products running on Apple’s latest software, which allows users to buy subscriptions to applications and easily buy add-ons like access to higher game levels or additional city guides.

“There’s going to be a lot more interest in iPhone applications after the upgrade,” said Greg Yardley, a co-founder of Pinch Media, a mobile analytics firm. “We’re going to see some really neat business models emerge because of the new ability to sell virtual goods.”

The increased interest in app developers is being driven by companies seeking to build cellphone apps for their products or services. They see it as a way to reach beyond the web for consumers. Though many apps are free, the willingness of people to pay 99 cents or more for one gives companies hope that apps may be a more reliable source of revenue than web sites.

“Companies are asking themselves, ‘How can we get on the iPhone?’ ” said Matt Murphy, a partner at Kleiner Perkins Caufield & Byers, which maintains a $100 million fund devoted solely to investing in start-ups creating apps for the iPhone. “Instead of trying to organically create their own property, they’re looking at applications with traction and cherry-picking the ones that seem like a good fit.”

With an instantaneous and established presence on the iPhone platform, he said, a company could tap into a stable, loyal fan base. For a big company that is trying to go mobile, and quickly, “those few million users are almost more valuable than the property itself,” he said.

That was the approach taken by IAC, which has more than 35 internet-based companies, including Ask.com, CollegeHumor and Evite. Last month, the company bought UrbanSpoon, a start-up based in Seattle that recommends nearby restaurants, for an undisclosed sum.

It is one of the App Store’s most popular products, having been downloaded close to five million times.