You don't need ICS if you're already connecting through a router. ICS would be overkill and unnecessarily complicated (secondary network, DHCP server, firewall, etc.). You just need a bridge.
Patch the ethernet port of the VOIP adapter to the ethernet port of your laptop. Then go to Network Connections (Start->Run, type "ncpa.cpl" (no quotes) and hit enter), select the two connection, right-click, select Bridge Connections, you're done.
Of course, for the long haul, you'd be better off to just buy an inexpensive, standalone, wireless ethernet bridge.
I'm not sure I understand what you're asking? You can access your VoIP provider over WiFi by using a WiFi VoIP phone, such as the Unidata WPU-7800 or the Cisco SPA525G2. What are you trying to connect to your Vonage router for if you have the WiFi access?
It has been released for the iPhone platform, which allows you to make Internet calls on the iPhone, saving you lots of phone bills Voipdito Small Business VoIP