This may be the way to go
BR121E - DYNAMODE - ROUTER, WIRELESS N + 3G, PORTABLE | CPC
You should be able to plug the vonage phone into the ethernet port and then use this as a bridge to the wireless network. It will run on either mains or battery power
You can also use it as a G3 wireless/ethernet modem router, just plugging in a USB dongle. However be warned - the instructions are useless.