Modem, Router, VoIP madness.

[mattkime]

static addresses - some routers allow assigning IP addressed based on MAC address. You can also set the client machines to "Using DHCP with manual address" and then type in the IP address manually - select something outside the range of what the router is assigning.

Look for "DHCP server"

you probably need to call vonage to make sure you're correctly configured.