This morning I sealed off the last hole in our wall (the old phone jack). And I'll show you how to as well:
First, leave the phone off the hook. Why? Well since you asked, there is a little tiny bit of electricity running through the telephone wires which is no biggie, but if the phone rings then you might get a shocker. Since turning off the breakers won't do anything, I believe this is your only choice. If not, it's got to be the easiest.
Second, separate and strip the wires so that they are nice and tidy. I've got 8 wires, for 2 phone lines. We're only going to use 1 line so I'm going to seal off the extra wires.
Tip: phone wires are 20 gauge, so use the tiniest notch in your wire strippers. Hopefully that saved you some time. Like 7 seconds.
Second, screw the mounting bracket into the outlet junction box for the faceplate (keep in mind how you want the faceplate to be positioned, you probably don't want that on crooked):
Next, hook up your wires. They are color-coded for your wiring convenience.
Lastly, mount the face plate and test the sucker out. That's right hang up the other phone, plug it into your nifty new jack and pick up the phone. Dial tone = success. Silence = fail. And you'll only have yourself to blame.
Congrats, you probably saved yourself some money.