While there is still no sign of the feature to allow global screenshots to be taken on your WP7 device, Smartphone France has posted a sneak peek at a solution (for those with registered/unlocked devices) that doesn't require the emulator to be used.
Using the Windows Phone Device Manager, developed by Julian Schapman, in conjunction with his app 'TouchXperience' one is reportedly presented with the ability to take screenshots on their device. Requiring the form of multitasking, this is a fantastic feature to bring to the homebrew table. The guys at Smartphone France proved their word by taking a bunch of screenshots on their LG Optimus 7 (some posted above).
Currently the Windows Phone Device Manager and TouchXperience for WP7 are both in active development and closed beta testing (only donators are eligible for enrolment). We will keep an eye on the development of the tools and apps, along with the features made available to users and keep you in the loop.
Source: Smartphone France
