When these folks call, if you are on your work-desk phone, after they ask for someone...then say, "Sure; absolutely. I see him in the office room right now. Hang on while I transfer your call." Then transfer the call to their own telephone number (the one they called from). Since that number is going to be a call-center number (going to multiple phones on their end), they will end up talking to one of their own people. :)