clcktwr

You have a setup for phones on following page.
http://www.instructables.com/id/Use-your-cell-phone-through-your-home-phone-wiring/step3/I-paid-for-these-jacks-Im-gonna-use-them/
You said, "But, in theory I could use these same phone jacks for networking or VOIP phones, although I'd have to replace this dumb jumper block with a small network switch."

Here's my setup which works perfectly. I have Verizon's FIOS with a cable to wireless/ethernet modem. Into that broadband modem I have a Magic Jack Plus. It has three connectors. The LAN port is to the modem's LAN port, the USB port goes to a power device which is plugged into AC power at wall, and the RJ-11 phone port is plugged to a wall jack using a splitter so I can keep a standard phone on that jack too. I disconnected the incoming "landline" which makes my internal wiring free from the grounding out that was causing. All old style phones work just fine in the home same as when they were connected to Verizon's landline. This allows me to use Double Play with Verizon instead of needing Triple play. Into one phone jack I have a Panasonic DECT 6 station plugged and that allows me the use of 4 other phones around the house. Almost every room has it's own phone now, including those which don't have a wall jack, and all wall jack phones still work fine. In fact, the phone service is better now since the old copper landline wires coming to house were 50 years old and spazzed out almost every heaving rainstorm. This setup allows plenty of phones around the house with no long distance charges anymore, allows wireless connect for several computers used, and wireless service for my guests with a laptop. Furthermore, I tested the phone lines using a dialup modem on an older computer I repaired for a friend through this Magic Jack Plus system to connect to a Juno server and that worked great too.

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