The popularity of iPhone apps has opened up a market for developers and entrepreneurs to sell content and services through apps. This is great technology news for entrepreneurs building web-based businesses.

Last Thursday, Apple informed developers in a letter that in-app purchases are now permitted in free apps, Wired.com reported.

"In App Purchase is being rapidly adopted by developers in their paid apps," Apple told developers. "Now you can use In App Purchase in your free apps to sell content, subscriptions, and digital services."

Now, entrepreneurial web developers can turn their iPhone apps into online stores for selling anything, such as upgrades in content and games. As an example, now makers of a free game app could offer a subscription service.

The spread of iPhones and other mobile smartphones from different wireless companies has built a new marketing venue as well, with mobile search growing to huge amounts of data. Entrepreneurs are also designing new search engines to rival Google and Bing, with mobile answer engines accessible on cell phones.