Microsoft is preparing for its General Distribution Release 3 (GDR3) update for Windows Phone 8 and some leaked screenshots now detail the upcoming update.

The upcoming GDR3 update is reportedly designed mostly for upcoming devices such as the much-rumored Nokia Lumia 1520 Windows Phone phablet, but it will also add some features for existing hardware as well.

Although the update is not out just yet, a WP Central forum member claims to have the GDR3 installed on his newly-purchased Windows Phone device bought off Craigslist.

The tipster offers several screenshots that picture the new Driving Mode feature, which is designed to automatically mute calls and texts when the device is paired to a car via Bluetooth or manually from the settings options.

One of the most notable new features, however, apparently allows users to close apps in the multitasking view. Windows Phone users have often requested such a feature and it seems that Microsoft took those suggestions into account with its new GDR3 update.

The screenshots further show a screen rotation option, and the Windows Phone platform will reportedly get several other neat additions. Other changes include built-in support for custom sounds on text, email, voice mail and reminders, something that was not previously available. Moreover, the GDR3 update will also allow WP8 users to restore from backup via Wi-Fi during initial setup.

The newly-leaked screenshots seem credible and fall in line with expectations for the GDR3 update. The folks over at The Verge also vouch for the authenticity of all images.

"The Verge can confirm that all the screenshots and features are genuine. Microsoft is currently testing the update, which will debut first on the Nokia Lumia 1520 and a HTC Harmony device, and is expected to start rolling out to existing devices later this year," reports the publication.

If the screenshots were not detailed enough, a new video has also surfaced online, showing the GDR3 update in action on a Nokia Lumia 920. The video clearly shows the new multitasking feature, so check it out below. Considering that the rumored Nokia Lumia 1520 phablet is expected to make its big debut on Sept. 26, the update should be ready soon enough.