I don't know how long it will last, but Assassin's Creed and Earthworm Jim are both free on WP7 and probably WP8.
Just downloaded Earthworm Jim. Already had Assassin's Creed, so I can't confirm if it's still free.
Source: http://www.trueachievements.com/n12260/pair-of-gameloft-games-free-on-windows-phone.htm
Just downloaded Earthworm Jim. Already had Assassin's Creed, so I can't confirm if it's still free.
Source: http://www.trueachievements.com/n12260/pair-of-gameloft-games-free-on-windows-phone.htm