Many cell phone providers give customers the option to keep their cell phone numbers private for all outgoing calls. When people dial *67, they are blocking their cell phone number from that particular caller ID for that call only.
Some people are more sensitive about their privacy, but don't know where to begin to start blocking a cell phone number. Did you know all it takes is a simple call to your cell phone provider? Ask your customer service rep to add cell phone blocking to your list of optional features. You can add this yourself. Just log into your cell phone account on the Internet, and change the settings there. Go to the Add/Change Features section and check the Caller ID Blocking box.