Adding a WRTP54G to an existing network
The WRTP54G can be brought with you to another location and used provided you can connect it with a wire to an existing router that is connected to the internet. The Vonage phone line will work if the existing network and ISP are configured to allow it.
First the theory. Downline of the WRTP54G, you have your own network. Upline from the WRTP54G, you will be connecting into someone else's network. That is the basis of the internet, a connection of networks.
Let your WRTP54G assign IP addresses for downline computers, either wireless or wired. Initially set the WRTP54G to get its IP address from the network to which it connects upline.
Connect the WRTP54G from its internet port to an available existing network router LAN port using a crossover cable. Make certain the DSL/Cable modem, existing router, and WRTP54G are turned off while connecting all cables. Then turn the DSL/Cable modem on first, existing router second, and WRTP54G last.
It will take several minutes for everything to boot. On the WRTP54G, confirm that the power LED and Internet LED are on. If you enabled wireless, then that LED should be on. If you signed up with Vonage and your internet phone worked, Phone 1 LED should be on. Try a phone call at this point.
At any Windows computer downstream of the WRTP54G, run ipconfig and confirm the WRTP54G as the computer's gateway. The default local address for the WRTP54G is 192.168.15.1. That is the address to use from the downline side to access the WRTP54G configuration http page. It is also the address that will show as the gateway URL for downline computers.
Be patient. You may have to reboot a few times, including your computer, to get everything working. For me, I can surf, function within Citrix sessions, and talk on the internet phone at the same time using the configuration described above.
If you cannot surf or use the phone and can modify the router configuration to which you are attaching the WRTP54G, you may try enabling DMZ or port forwarding on the upline router. These configurations requires a static IP address assigned to the WRTP54G within the range of IP addresses acceptable to the upline router and an IP address not already assigned to another device connected to the upline router. In my configuration I did not use DMZ nor did I use port forwarding and everything worked fine.