A Web-based civic action site is providing a way for people irate about the Stop Online Piracy Act (SOPA) to voice their opinions in a very literal way. Reverse Robocall, a site set up by Shaun Dakin and Aaron Titus, allows users to record a message through the site and perform their own robocalls to politicians and lobbyists.

For a fee of $10, Reverse Robocall will let you record a message that will be delivered as a phone call to the offices of the co-sponsors of SOPA and each of the associations and lobbying groups that have backed the bill in Congress—88 in all. You can even customize the phone number that will appear in caller ID for the call in order to avoid being blocked by systems that reject calls without them. And, if you choose, you can let others listen into your message on the site and rate your effort.

They sell different products. $10 gets your message sent to 88 offices. $25 gets your message sent to everyone supporting SOPA and PIPA

http://www.reverserobocall.com/products/sopa-and-pipa-proponents-301-offices

I don't think you get any assurance that the messages are actually delivered other than what is listed under their "Our Responsibilities" section.