It’s just a recent rumour about the windows phone 8. WP7.8 currently does take screenshots but only with dev-unlocked devices. For the general consumers it’s just not possible. Not even with apps. Now every platform can now take screenshots in a much easier fashion. Whilst Symbian might not have it built in, it does have a few apps that will allow for that function.
It’s not technically a mainstream feature, but it’s just nice to have that option.
WP Dang reckons that WP8 will have this finally in a Windows Button + Camera Button combo.
Is that a good button combination? In the comments, the poor translation seems to suggest this might appear in WP7.8 too.
As well as taking a full screenshot, like a screenshot function like of Symbian have a print screen option.
Such a feature would be beneficial for developers for promoting their apps, consumers for sharing bug reports and those in the tech media who need images for reviews. Currently, there is a hombrew option for those with developer unlocked Windows Phones. It requires sideloading of a XAP file and while it is very effective most Windows Phone users are unable to use it due to the requirements. Simply brilliant and a must have for anyone who is dev unlocked.
Grab the app here at XDA.