In the past, software makers for the PC would develop software primarily for Windows or Mac OS; the choices were limited. For mobile phones and smartphones, however, app development is far more complicated, as BusinessWeek reports.

Companies joining Apple in the crowded field of mobile app stores include Nokia, Microsoft, French carrier Orange, Samsung, and German provider Deutsche Telekom (DT), just to name a few.

As BusinessWeek explains, the various OS formats provide lots of choices for consumers and steer clear of monopolistic OS battles that plagued the desktop in the 1990s, but they will give software developers a headache as they try to reach the various platforms -- in fact, they may skip some altogether.

Which platform do they target? "When someone comes out with a new device, you just have to go with your gut," MySpace CEO Chris DeWolfe tells BusinessWeek.