A number of companies are using this week’s Mobile World Congress in Barcelona, Spain to announce their own mobile software marketplaces, in hopes of duplicating the success of Apple’s “App Store.”

Microsoft CEO, Steve Ballmer, unveiled the Windows Marketplace yesterday, saying that the ability to purchase and download software would bring Windows-based smartphones to “another level.”

“It’s no longer about how the phone works by itself but how it works with the internet,” Ballmer explained. “It is your instant access to all the people and information that you care about.”

Finnish cell phone giant, Nokia, also announced a mobile application store yesterday, and plans to use a very similar business model to Apple’s, collecting a 30% commission from software developers.

Carriers and device manufacturers are eager to cash in on the mobile software marketing phenomenon, in the face of declining mobile phone sales and cutthroat price competition in the wireless voice business.

“Every man and his dog wants an apps store,” commented Ovum principal analyst, Tony Cripps. “Apple’s has been such a phenomenal success that all the other players are desperately trying to play catch-up as traditional revenues fall.”

This trend could create new competition between handset makers and carriers, given that UK-based O2 and French-based Orange are both launching software marketplaces of their own. (Both O2 and Orange have contracts to sell Apple’s iPhone and numerous Nokia devices, meaning that some users will have more than one app store to choose from.)