Microsoft Corporation has definitely said it will launch Windows Phone 8.1 for existing Windows Phone 8 handsets on June 24.

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It also pledged to support its flagship smartphone to be able on the new software version for at least three years after launch.

Microsoft also promises to include incremental updates during this three-year period.

On its support lifecycle webpage, Microsoft's listed a lifecycle start date of June 24 and a concluding date of July 11, 2017.

The company did not, however, guarantee that all Windows Phone 8.1 handsets will support the next version of Windows Phone, which is widely believed to be Windows Phone 9.

As is the usual, the actual availability of the updates should vary from model to model and by carrier.

It should be remembered that the distribution of the updates is usually manipulated by the mobile operator or the phone provider.

This means that even if you own a Windows Phone 8 smartphone, you might not receive your system update on June 24.

Carriers normally need weeks or even years to verify a software update for security and compatibility with carrier-published apps. Some might not push the update at all.

Microsoft announced Windows Phone 8.1 in early April. The star of this upgrade is Cortana, Microsoft's digital assistant and its answer to Apple's Siri and Google Now.

Windows Phone 8.1 also features pull-down notifications, WiFi and battery-management tools, among others.