Microsoft just announced today's release of the Windows Phone 7.8 SDK, which should be a wee bit helpful for developers wanting to test their apps and Live Tiles with the revised OS. The new SDK includes two software images (build 8858), one that simulates devices with 512MB of RAM and another for 256MB handsets. The primary purpose of this release is to let developers test their Live Tiles with Windows Phone 7.8, which supports resizable Live Tiles. While it's not much of a surprise, the new SDK includes no new APIs over the Windows Phone 7.5 SDK, which further reinforces the impression of Windows Phone 7.8 as a largely cosmetic update. On the plus side, legacy support is alive and kicking, as Microsoft promises the SDK update won't alter existing Windows Phone 7.1 emulator images. For more details of this release, be sure to hit up the source link.
Microsoft Windows Phone 7.5