Om presents an interesting case about Clearwire. While they have admitted to blocking Vonage one has to remember that they are still in trial mode. My guess is they will come around and offer two tiers of service.
One that is more of an AOL walled garden approach, while the second, and at a higher price, delivers the customer unfettered access to the Internet.
As an FYI, Metricom in their Ricochet days tried to limit what could run over their network too. They wanted to bar streaming media over the net using their wireless network. Clearwire would do well to look at the past and see their future.