Yes I know the post is close to 2 years old.  My comments are for future readers.

*67 does not work when calling toll free numbers or government number.  It generally works for other numbers.  However, if they have a sophisticated enough phone system, then the *67 does not work.  I have used the prefix before for some telemarketers and they could still see my number.

*67 is a good precaution, but it does not guarantee your anonymity.