Peter Davison has uploaded two fantastic videos that he made for the Gallifrey One fan convention in 2010 and 2011. David Tennant features in both videos.
You can follow Peter on Twitter here.
Peter Davison's 2010 message to Gallifrey One from Peter Davison on Vimeo.
Peter Davison's original video message to Gallifrey One 2011 from Peter Davison on Vimeo.