Yesterday, The Wall Street Journal reported that Microsoft plans an app store of its own.

The news follows similar on-device and platform-specific app stores unveiled by mobile phone makers such as Apple, Research In Motion, Samsung, Google, and Palm.

Microsoft CEO Steve Ballmer will make a series of announcements at the Mobile World Congress conference in Barcelona on Feb. 16. As Microsoft looks to make headway in the mobile market, it faces some tough competition from Apple, Google, and others.

Meanwhile, Nokia may also open an app store at Mobile World Congress.

Apple's App Store for the iPhone has been a runaway success. It now contains more than 15,000 apps and downloads have surpassed 500 million.

As for RIM, it is now accepting submissions for its BlackBerry Application Storefront, which is expected to launch in March.

Rumor has it Google will soon offer paid applications at its Android Market for gPhones like the T-Mobile G1. Users can currently only download free programs directly to their Android-run smartphones.

Palm's on-device app store allows you to download 5,000 apps and games -- including 1,000 for free -- from a Palm device such as the Centro or Treo Pro. It requires a download of the app store software from PocketGear, which is the hosting store. And it contains both Palm OS and Windows Mobile programs.