Freepbx siptrunk exchange

I have successfully config. a sip trunk to my exchange server (with outb. route) but it looks like that exchange did not get the called number from the freepbx because on the exchange I hear only the standard message (asking for the user) and not my config. user voice box.
Could that be a problem of the trunk or ou route config?
Have not any Idea at the moment.
Thanks for help