Bill wants to sign up for Vonage, and he's using WiMax and a Clearpoint router. Leo says that if he can get a consistent 512MB/s up, then he can use Vonage for voice over IP calls. WiMax is probably not that consistent though.
Obihai may be a better option, but he wouldn't get any 911 service with it. It's free with a purchase of the VOIP hardware itself, and uses Google Voice.