That is not the case and never has been. In the US, at least, ISPs are not common carriers, have never been common carriers, and never will be common carriers unless there's a significant change in the law. ISPs owned by telephone companies are not common carriers, even though their sister telcos are.
The legal responsibility of ISPs for the material they carry has nothing to do with the amount of traffic control they exert and everything to do with specific laws on the topic, notably the CDA (47 USC 230) and the DMCA (17 USC 512).
I don't know why the myth about ISPs being common carriers keeps reappearing. It's not like it's hard to find out.
With respect to alleged VoIP blocking, my ISP happens to be a subsidiary of my local rural telco, and I just cancelled my Vonage service due to a combination of voice quality that went into the toilet and Vonage's complete failure to provide any support when I tried to e-mail or call them. But having done a fair amount of packet traces, I'm quite sure that this has nothing to do with my ISP and a whole lot to do with congestion at routers within NSPs and particularly the gateways between the NSP that my ISP uses and the one that Vonage uses. I switched to Lingo and their voice quality is OK.
Regards,
John Levine snipped-for-privacy@iecc.com Primary Perpetrator of The Internet for Dummies, Information Superhighwayman wanna-be,