Apple (NSDQ: AAPL) said last week that the iPhone App store has now hit 15,000 applications and half a billion downloads, so it’s no wonder that other device manufactures are ramping up their competitive services. Blackberry-maker Research In Motion has already announced their intentions, and is looking to launch its storefront soon. GigaOm reported today that the company took a major step forward when it started accepting applications from developers that would allow their applications to be included in the new Blackberry Storefront.

Separately, it looks like rumors are heating up about what Microsoft (NSDQ: MSFT) has coming at Mobile World Congress in February, and it appears the giant is getting ready to roll out a number of “Sky”-branded products in direct response to Apple’s App Store and MobileMe offerings. According to Neowin (via MobileCrunch), there will be three offerings: SkyBox, which syncs contacts, SMS, email, calendar items and pictures over-the-air; SkyLine, which is the enterprise version of SkyBox; and SkyMarket, which is Microsoft’s response to RIM’s storefront, Apple’s App Store, Google’s Android Market, etc.