Mobile application developers are in for busy times ahead.

According to a recent report by In-Stat, mobile phone manufacturers will be pumping more than 100 million mobile app store-compatible phones into the market within five years.

That’s 100 million phones capable of downloading mobile applications of every ilk, and that’s good news for mobile application developers.

The research points to Apple iPhone users as the most active mobile app store users, significantly outpacing users of BlackBerry, Palm OS or Windows Mobile phones. However, as more enterprises adopt the smartphone as a must-have business tool and more enterprise applications are created for mobile devices, future usage is forecast to be driven equally by business applications.

However, when it comes to mobile marketing, current application marketing “lacks consistent, accepted analytics many advertisers are accustomed to,” according to the report – a problem shared by most new forms of advertising media. With the expected glut of new applications hitting mobile app stores, developers and marketers must come up with ways of differentiating their product and getting it noticed.

“With greater capabilities in both running native applications and viewing ‘real Internet’ Websites, smartphones have increased usage and user expectations for mobile content,” said David Chamberlain, In-Stat analyst in a prepared release. “Along with the expanding handset base, users are downloading more applications. Reach for marketing applications is growing rapidly and those applications can provide prolonged engagement with the user and keep the advertiser’s brand in focus.”

Mobile application stores seem to be hogging the mobility spotlight. During the GSMA World Mobile Congress in Barcelona in February, Nokia and Microsoft both announced their intentions to open an online applications marketplace available directly on their devices.

Service carriers such as Sprint, AT&T and T-Mobile all have versions of online app stores, but the trend is now turning toward manufacturers offering downloadable apps.

Michele Pelino, senior analyst at Forrester Research, noted that the actions of the mobile hardware and software vendors reflect a natural progression of the technology.

“They realize there isn’t a seamless way for apps to go across all vendors,” she said. “Because of the fragmentation of the market, there is no easy way to write one application that will work on every device, and they recognize their devices are only as valuable as the applications you can use with it.

“Vendors recognize they have to have the devices out there, they have to have the applications created by third-party vendors, and they have to have these applications all in one place – that is the real benefit of having these sites,” she said.