A former student, Joshua Marsh, who actually knows something about the technical side of these things (always something we lawyers sedulously eschew), points out a technological arms race this port blocking creates that maked port blocking futile:
The technology behind VOIP makes this interesting. Vonage and many others are using SIP for VOIP. But that isn't everybody. [Where I work is] currently using Cisco's VOIP solution which is not (natively at least) SIP based, so my VOIP works fine over Clearwire. Additionally, if I connected to any VOIP provider over a VPN, there would be no way that they could block the traffic, because to them it would appear only as an encrypted IP packet. I could be accessing my intranet or streaming voice/video. I think this points out the futility in any such blocking attempt. Surely a move that is not far off for Vonage and other providers is having VPNs built into their software. They will then have the added advantage of being able to claim highly secure voice communications.
This is interesting on two fronts. One, it indicates the difficulty providers' will have on IP platforms in pulling off the (necessary and beneficial) price differentiation based on service bundling and blocking. My colleague Adam Thierer thinks that broadband markets eventually will end up price differentiating based on bandwidth usage, in part because of the futility of differentiating based on service bundling. Two -- to make the obligatory ideological point -- this technological work around obviates the need for any net neutrality regulation because the technology and market competition yield that result, without the regulatory costs and rentseeking incentives.