I'm usually ok when people find out my number, but there are times when I'd rather not have the person on the other side know my cellphone number. Such as when I call someone, hit the answering machine and hang up. I had a clunky old Motorola phone that must've weighed one or two pound and there was a feature to block my number on next call. I have a Motorola 120c now. It doesn't have this feature, however I am using a different carrier as well. Is it dependent on the phone or the carrier?
