It is possible for your caller ID to appear as "anonymous" on the receiver's side by dialing a certain dial sequence. This works for most but not all telephone networks that allow anonymous calling.
Simply dial *31* in front of the number you wish to call.
For Example:
Local Telephone Number: 68175600
Anonymous Call: *31*68175600
International Telephone Number: 60387764312
Anonymous Call: *31*6038776431