Call 1-866-243-4357 for Vonage tech support.
Otherwise, if you know anything about vonage, treat the vonage box like any other router. Preferably connect it directly to your modem and put any other equipment behind it. If that's not possible, try to set up QOS on the router in front of it. If you need to use port forwarding, vonage service typically uses ports 5061, 10000 and 10050-10150 UDP.