The CEO of Vonage has been arguing that port blocking of SIP traffic is censorship:
Port blocking of VoIP traffic, he opined, is a step down a slippery slope that could lead to network owners blocking content or Web sites they disagreed with.
Mr. Citron fails to notice that at least one of his indirect competitors is not having these issues since they don't use SIP but rather a custom encrypted protocol. Of course the whole point of SIP is a standardized way to do VoIP which combined with supposed end to end connectivity of the Internet itself gives advantages over propertiary stuff. Of course Vonage can choose to use different ports which still doesn't change the main protocol or even better run the SIP stack over IPSec (which with IPv6 would be redundant). But their solution is different:
While Citron doesn't quite know what the next step will be, he is hoping that the FCC uses some of the enforcement tools at its disposal to strongly discourage the practice of using networking technology to selectively block, alter or impede Internet traffic.
Of course one side effect of this would be is that if such rule were passed providers would be forbidden to block outbound port 25 traffic to block spammers, or defend against DDOS attacks. Unfortunatly, it is more likely that the legal measures will lead down a slippery slope rather than technical.