Microsoft has announced the release of the Windows Phone 7.8 SDK, giving Windows Phone developers the ability to update their apps to be compatible with the new version of the operating system. Windows Phone 7.8 does not support Windows Phone 8 apps, but developers that have written apps for Windows Phone 7.5 can now update those apps with Windows Phone 7.8's new customizable Start Screen features. Apps built for Windows Phone 7.5 mostly run the same on 7.8, but developers can now take advantage of the Windows Phone 8-like small, medium, and large Live Tiles when the app is used on a 7.8 device. The SDK also lets developers test their apps on both low-end devices with 256MB of RAM and higher-end models with 512MB or more of RAM.
Windows Phone 7.8 has been more or less off the radar since Windows Phone 8's big debut, but Microsoft notes that there are a few devices with Windows Phone 7.8 shipping in various parts of the world. Unfortunately, existing devices with Windows Phone 7.5 have not yet been updated to 7.8 and it's still not clear as to when exactly that will happen, although Microsoft did promise that it would be coming early this year. But owners of the Nokia Lumia 900 and other Windows Phone 7.5 phones can be assured that when that update does eventually arrive, their apps should be compatible with the new platform's features. Assuming the developers have bothered to update them with the new SDK, of course.
Windows Phone developers can grab the new WIndows Phone 7.8 SDK from Microsoft now.