Mobile application marketplaces are all the rage right now, and speculation is mounting that at least two more handset giants are preparing to introduce similar services next week.

In what appears to be a slip up, US software firm Microsoft pushed the holding page for its My Phone web service live this week.

According to the site, Microsoft My Phone syncs information between a user’s Windows mobile phone and the web, paving the way for backup services, photo publishing and social networking tools.

However, many expect that an app store, much in the vein of Apple’s successful marketplace, will also be announced at Mobile World Congress in Barcelona next week.

Similar rumours are also circulating about Nokia’s plans for the show. It’s long been thought that the Finnish vendor was working on an extension to its own Ovi platform that will act as a marketplace for mobile applications for Symbian.

Along with Apple, the Open Handset Alliance (OHA) has introduced Android Market for Android, while BlackBerry maker Research In Motion (RIM) is known to be working on its own Applications Storefront, and Samsung has its Mobile Applications platform.