Have you had a chance to try out caller ID spoofing yet? If not, you can do it for free AND you can change your voice during the call.
To try caller ID spoofing for free visit www.spooftel.com/freecall/
You don't have to deposit any funds to try it out. If you end up joining SpoofTel, you can use their other features like SMS Spoofing, Fax Spoofing, Call Recording, and the sound boards.