VOIP gizmo placement in network

Good Day,

I have an old Sunrocket Gizmo which I want to use for the GrandCentral - Gizmo Project setup for free VOIP calls.

I have a Motorola 5100 cable modem with Comcast.
The Sunrocket Gizmo is a InnoMedia 6328.

I would like to have the Gizmo setup between the cable modem and my D-Link DI-604 router.

I ran ethernet out of the cable modem into the WAN plug in the back of the Gizmo.
I ran another ethernet cable from the LAN plug in the back of the Gizmo into the WAN input of the D-Link router.

I don't get any internet connectivity or phone signal.

I also tried running from the LAN plug in the Gizmo to one of the 4 numbered LAN jacks on the D-Link router.
Still nothing.

The only way I have been able to get it to work is to run ethernet from the cable modem to the WAN port of the D-Link router. I then run out of the router with one of the 4 numbered LAN jacks to the Gizmo. Both the WAN and the LAN jacks on the Gizmo work this way.

Any ideas of how I can get the Gizmo working outside of the router?

Thank you for your assistance!