WhatsApp has announced that it is ending service to millions of smartphone units due to compatibility issues.

The popular messaging application currently has more than a billion users. However, due to technological advancements, compatibility issues with other phones will result in the termination of service to some users.

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A spokesperson for WhatsApp said; "While these mobile devices have been an important part of our story, they don't offer the kind of capabilities we need to expand our app's features in the future."

For Apple users, the application will no longer run on the iPhone 3GS, a second generation device launched in 2009. Devices with iOS6 such as iPhone 4, 4S and 5 will also have to be updated to iOS 10 to enjoy the app.

For Android users, the 2.1 and 2.2 version of the operating system will no longer be able to run WhatsApp. This means that smartphone units, which were launched between May 2010 and Nov. 2011, would not support the messaging application. The Windows Phone 7 is also affected after Microsoft dropped its operating system in 2014. Blackberry OS, BlackBerry 10, Nokia Symbian S60 and Nokia S40 are also on the list of outdated systems.

WhatsApp was launched in 2009 and became the best-known messaging platform across the globe with its video call and end-to-end encryption features. 

The deadline for the outdated smartphones is set at the end of this year. However, WhatsApp has extended support for Blackberry and Nokia until June 30, 2017. Users are advised to have their devices' operating system updated before the year ends.