The mobile app market for devices such as Apple’s iPhone and Google’s Android platform is already growing fast, but could expand even faster over the next two years as more consumers join the smartphone party.

A study conducted by the mobile app service Getjar claimed that downloads would increase from about seven billion in 2009 up to 50 billion by 2010, according to the BBC. The study also noted that the number of mobile app stores has grown from four in 2008 up to 48.

Interest in mobile apps has been growing as more smartphone models ship, and while that means more mobile app sales, Getjar expects Apple’s App Store will eventually lose share to competitors.

The way apps on mobile devices generate revenue is likely to change, according to the report. Currently, most companies get revenue by selling their apps to customers, but that’s expected to slowly transition into an in-app advertising and virtual goods sales model.

Getjar also expects that “feature phones,” or mobile phones with limited functionality compared to smartphones, is the wave of the future, too.

“We wanted to find out the real value of the industry because we felt certain segments like the iPhone were being over-hyped and so-called feature phones were being under-hyped,” commented Ilja Laurs, Getjar founder and CEO.

The notion that the smartphone market will succumb to limited feature mobile phones seems unlikely considering the growth in the market. The idea that the mobile app market will continue to grow at a staggering rate, however, seems far more likely.