Always test as much as possible before relying on any technique to block Caller-ID. Some of these methods to block Caller-ID work in some areas, but not in others.
Block Caller-ID For a Single Call Using a LASS Code
Dial *67 before you dial the number. (141 in the United Kingdom)
Block Caller-ID On All Outgoing Calls
Dial your local telephone company and have them add Caller-ID block to your line.
If you use this method to block Caller-ID, you will have to dial *82 before every call for which you do not want to block Caller-ID.
Block Caller-ID Using Operator Diverting
Dial the 0 Operator and have him or her place the call for you.
Block Caller-ID Using a Pre-Paid Phone Card.
Dial the call using a pre-paid phone card.
Block Caller-ID Using A Commercial Caller-ID Blocking Service
Dial through Security Consultants at (900)PREVENT for U.S. calls ($1.99/minute) or (900)STONEWALL for international calls ($3.99/minute).
If All Else Fails, Block Caller-ID By Leaving the House
Dial from a pay phone. 😉