How do we get ISPs classified as common carriers?

Sue their pants off for the copyright infringement of their customers (and all the other illegal things customers can do). This why common carriers exist. They trade ultimate control over the transfer of content and treat it equally for the protections of being indemnified from the content itself. This is why the U.S. Postal Service can't be prosecuted for transporting a death threat letter. Make it about money and they'll jump on the common carrier bandwagon before you can blink.