During Microsoft’s Windows Phone Summit today, Microsoft revealed that existing Windows Phone 7.5 users will receive an upgrade to Windows Phone 7.8, and not Windows Phone 8. Since WP8’s main features involve new hardware, certain features will not work on existing devices, that’s where WP7.8 comes into play.
Windows Phone 7.8 will come with the new Start Screen that was seen in Windows Phone 8, which includes re-sizable tiles and the removal of the gap on the right side of the Start Screen. We will also see new colors for the tiles. Current phones, such as the Nokia Lumia 900, are unable to take advantage of the new features in Windows Phone 8, due to the legacy hardware. Microsoft hopes to provide the same experience on legacy hardware that you would see in Windows Phone 8.