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 팬 outside the stage door. Apart from those (where you'd only be able to have a few 초 with him) there really is no way 팬 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 당신 are in, if he happenes to be a guest 또는 guest dj on a radio program were 당신 can call in and speak with him.

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

but otherwise I don't have a clue.