I see that when there is an emacs server without a visible frame, 

emacsclient --eval "(org-mobile-push)" , gives the error :

Only when there is a visible frame does org-mobile-push succeed. Is there a reason why org-mobile-push needs a frame ? How can I make it work without a frame?

Org version is 8.3.2, emacs version 24.4.1, Debian Linux 8.2.

thanks