YES YOU CAN.
You can set up your Frontier or Verizon Actiontec wireless router to use WEP if you want to. In my case, the wireless network was already in use at the customer's home, and there were quite a few WiFi devices already configured to use 64-bit WEP. They didn't want to switch to WPA (which would have forced them to change the WiFi config on all their other devices!)
Please note that these instructions assume your router is using mostly "default" settings. If you were capable/experienced/technically adept enough to alter them, you should also be able to figure out where your settings differ from the defaults, and adjust accordingly.
You assume all responsibility for any alterations to your TV or router configuration. I'm simply sharing the steps I found to work for my situation.
At the TV:
Locate and carefully write down the MAC Address for your wireless adapter. You can find it on the Network screen from the TV setup menu. It will be a series of six pairs of hexadecimal numbers separated by colons, like "00:AA:00:12:34:56". All numbers and the letters A-F (or a-f) are valid. COPY THIS NUMBER CAREFULLY.
At the PC:
Login to the router. By default its IP address is 192.168.1.1, but yours may differ.
Click on "Advanced" in the top menu. You'll get a popup warning about changing these settings. If you choose to continue, click the "ARP Table" hyperlink under the toolbox list. A DHCP Connections list will open.
Click the link to "New Static Connection".
Enter a name for your TV. Like "Panasonic TV". Or whatever.
Enter the IP address you want to assign. I used 192.168.1.120. Be sure the first three octets match your network! And be sure the last one ("120" in my example) is not already in use. You could pick another one, like 50, or 210, or whatever you like, but I chose one that is high enough to probably never "clash" with the actual DHCP pool. Most homes will not consume 100+ DHCP addresses.
Enter the MAC Address from your TV's wireless adapter. This is like the "phone number" for your specific TV, and just like dialing a wrong number your TV will not connect if you enter the wrong MAC Address.
Apply your changes. You may close the "Wireless Broadband Router" window.
At the TV again:
Open the Wireless network config screen, and enter the SSID (or search for networks and pick yours). Then enter the WEP key you use on all your WiFi devices to access your network. Follow the onscreen prompts to test your connection, and verify that your TV now has an IP address, and can connect to the internet.
Hope this helps.