Unless something has changed recently, you can have a phone number "unlisted unpublished", which means that it won't be printed in the phone directory and directory assistance will not give it out. You can have an "unpublished" number, which means that DA will give it out, but it won't be printed in the directory. I don't know if the charges are/were different or not. I've always had mine "unlisted unpublished".
Regards,
Charles G. Gray Senior Lecturer, Telecommunications Oklahoma State University - Tulsa (918) 594-8433