Microsoft has released the Windows Phone 7.8 SDK as an optional update for developers. It brings two new emulator images to the existing version. This will give developers a chance to fully test how their Windows Phone 7.5 apps will behave with the re-sizable tiles which will be a part of the Windows Phone 7.8 update.Hopefully the release of the SDK would also indicate that the launch of the Windows Phone 7.8 software update for existing Windows Phone 7.5 devices will be coming very soon. Until now Microsoft has been very vague with the release date and said it will arrive in early 2013.
Windows Phone 7.8 primarily offers the re-sizable tiles which were introduced in Windows Phone 8. It also brings a few minor improvements like additional theme colors, Bing Wallpaper of the Day for your lock-screen and other security improvements. Nokia Lumia users will get added benefits like the Bluetooth Share and Ringtone Maker apps.
If you have been following our website, you would have known that the Windows Phone 7.8 update has been available to Nokia Lumia users for some time now, through Navifirm. You may have been able to follow our guide on how to install Windows Phone 7.8 on your Lumia device. If you haven't, you wont have long to wait to get WP7.8 officially pushed to your device through Zune.
Microsoft has also stated that new Windows Phones based on Windows Phone 7.8 are beginning to ship, which is good news for the update. But it does add some confusion. Microsoft obviously plans to continue to offer Windows Phone 7.x as an option for Windows Phones with lower end hardware. However they have refused to bring several modern features which are available on entry level Androids to Windows Phone 7.8. We hope that Microsoft’s plans to continue offering Windows Phone 7.8 indicates that they have more updates in store for Windows Phone 7.x
source – Microsoft