How can you block sending your phone no?

Pick up your phone, wait for the dial tone. Then dial *67, wait for the dial tone sound to like cut out twice. Not a beep but no actual sound for appxroximately 1 second each, one immediately after the other. When the dial tone resumes, make your call. This is a per call type of thing. In other Words, YOU control who sees your number. Do this for every 'annonomous' call you want to make.