Microsoft is pulling the plug on its Skype app for smartphones running Windows Phone 7

Microsoft, the world's largest software company, has undoubtedly gained immense success with its video calling service Skype, which is one of the world's most popular VoIP services and is available on all major platforms including iOS, Android, Windows Phone and of course desktops and Macs. But the latest update on Skype has left many users unable to use the app altogether.

The new change will be carried out over the next few weeks. Microsoft is not only dropping support for the app on Windows Phone 7, but is retiring Skype on its first generation of mobile computing platform completely. The announcement was made via Microsoft's Skype blog post, in which the Redmond-based software giant warned subscribers to cancel their subscriptions if they used Skype only on Windows Phone 7 platform. If customers have recently paid their latest subscription, Microsoft is offering a Skype Credit or subscription refund.

"We want everyone to experience the best Skype has to offer - from enhanced quality to better reliability to improved security - and the newest version of Skype is the way to do that," the company's blog post reads. "So everyone can benefit from the latest improvements, we sometimes retire older versions of Skype across all platforms, including mobile devices. For that reason, we are permanently retiring all Skype apps for Windows Phone 7."

With this, owners of smartphones running Windows Phone 7 have the option to purchase the latest handsets supporting Windows Phone 8 or 8.1 versions or upgrade to newer OS. But on competing platforms, Microsoft continues to offer Skype on older versions such as Android 2.3 as well as iPhone 4 running iOS6 and higher. This has upset many old WP users who cannot upgrade their OS to later versions. BlackBerry handsets with version 10 are also covered under Microsoft's support for Skype on mobile.

Skype video calling service is extremely successful, as users spend an average 50 billion minutes on it per month, according to the company's By The Numbers webpage. But letting go of Skype for WP7 users has sent a wave of disappointment and frustration, according to the comments on  PC World.

The retirement of Skype for WP7 comes shortly after the software giant retired its earlier version 6.13, which is used by most Mac owners running OS X 10.6 to 10.8. But the later version of Skype 6.15 is a replacement for Mac users.

Skype is available for download from Windows Store and requires at least Windows Phone 7.5 as the base OS.