Microsoft is preparing to update its existing Windows Phone 7.5 handsets to a 7.8 version before the end of the year. The update will bring the new Start Screen experience from Windows Phone 8 to existing handsets, but we've heard very little about any additional features. XDA-Developers member dotcompt has managed to create a custom ROM with the Windows Phone 7.8 update for HTC HD7 owners.

The ROM is very experimental and we certainly wouldn't recommend flashing it on a device, but it does include the new Start Screen and is described as beta software. Dotcompt says the ROM was dumped from a Nokia device running Windows Phone 7.8. We know Nokia is preparing to update all of its Lumia devices with Windows Phone 7.8, but there's no firm date on the release. Microsoft is not commenting on a potential release date or additional features for Windows Phone 7.8, but we may well see some additional details surface from this latest ROM leak. We'll update you accordingly if we spot any extra functionality over Windows Phone 7.5.