Microsoft announced an update to its Windows Phone 7.8 SDK, although it has provided little detail on when the platform will be made available to existing WP device owners.

The new release provides developers with two emulators, for developers targeting devices with 512MB or 256MB of RAM. However, it was also noted that there are “no new APIs available to Windows Phone apps in Windows Phone 7.8”, meaning additional features will not be supported.

Windows Phone 7.8 is an upgrade for Windows Phone 7.5 devices, which is intended to make the platform appear more like the later Windows Phone 8. The headline feature is support for Live Tiles, delivering content to the icons used to represent apps on the homescreen.

While the refresh has been criticised as being largely cosmetic, it will also support the distribution of apps in more markets.

So far, Windows Phone 7.8 is only available on new devices, rather than as an upgrade to existing smartphones. Some reports suggested the update for Windows Phone 7.5 devices will follow at the end of this month.