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?