Users of Windows Phone 7.5 handset, who have been leapfrogged with the release of the recent Windows Phone 8 operating system, could be in line for an upgrade from Nokia.

Leaked documents reveal that devices such as Nokia's Lumia 800 and Lumia 900, which currently run Windows Phone 7.5, will get the upgrade.

Microsoft has been criticized for not allowing Windows Phone 7 users from upgrading to Phone 8, and it looks like Phone 7.8 will offer a half-way-house between the two operating systems.

The leak was made on a Chinese Web site and reveals that the Windows Phone 8's customizable lock screen will make its way onto version 7.8, allowing users to select apps to push notifications and photo content to the lock screen.

The new version will also have an updated Internet Explorer 9 but a full update to Internet Explorer 10 won't be happening, at least not at the moment.

Windows Phone's Italian Facebook page has already promised support for Rooms (a new feature in WP8), SmartGlass and Xbox Music.

Nokia has been a leading developer of the Windows Phone platform and recently launched the first new devices to run Windows Phone 8 - the Lumia 920 and Lumia 820.

Both devices take advantage of the completely revamped operating system which is designed to seamlessly integrate with Microsoft's desktop operating system and its tablet devices.

The leaked document was from sales training slides shown to workers at Nokia China and Nokia, according to some translation, is training its sales staff to market Windows Phone 7.8 as "having the same user interface and experience as Windows Phone 8", and existing Lumia products will continue to receive updates from Nokia.

Some of the features which will be exclusive to Lumia users who upgrade are:

• Sharing of media via Bluetooth
• Ringtone creation app
• Upgraded contacts transfer app
• Upgraded contacts sharing app

Earlier, a Tweet from the official Windows Phone Twitter account in Brazil revealed that the upgrade will likely be available in the first quarter of 2013.

However, Windows 7.8 is far from an upgrade to Windows 8, and apps developed for the latest version of the operating system will not be backwards compatible.