how can i talk to him beside letters

Very occasionally he does fan/autograph signing events, and whenever he does a play, he signs autographs for mashabiki outside the stage door. Apart from those (where you'd only be able to have a few sekunde with him) there really is no way mashabiki can get to talk to him.

As far as I know, David Tennant doesn't have an e-mail account that is opoened to the public.

Neither is his phone number. LOL!

Well, depending on what country wewe are in, if he happenes to be a guest au guest dj on a radio program were wewe can call in and speak with him.

Or, wewe could try yo contact any studio au go through his agent c'mon! all actors have an agent.

but otherwise I don't have a clue.