You can choose not to have your phone number and name displayed on caller-id. You've probably noticed that many calls you receive show up as Private Number, Out Of Area, Anonymous, etc. on your caller-id display (damn telemarketers). These numbers are said to be blocked.

Keying *82 before keying the rest of the number you're calling unblocks this information, allowing your phone number and maybe your name (from non-cell numbers) to show up at the other end.

Follow the link to see more codes, or do a Google search for star codes.

If you push *82 before calling it unblocks you phone number (provided that you initially have it blocked) and allows the callee to see your number on caller ID. Conversely, If you push *67 it will block your number from being picked up.