Hooking up a phone line to an existing outside box is a fairly simple procedure. It's a great way to add an additional phone jack to a spot in your house where you've always wanted one. Save yourself a bunch of money on labor and travel charges the phone company would tack onto your bill, and do it yourself.
Locate the outside phone line box on your house. It should be centrally located. You may have to follow the interior phone wiring to locate it, but it should be pretty obvious to find. Lift the panel of the phone line box upward.
Lift the clasp holding the black plug into the test jack. Remove the plug from the test jack.
Slice through the end of your phone line with a razor about 2 inches down to expose the four color-coded wires inside--red, green, yellow and black.
Strip the tips of each of the color-coded wires about 1/2 inch down, and twirl the exposed wire to tighten it.
Place the phone line (with the stripped ends) up through bottom of the phone line box and into the access portal.
Line each color-coded wire up with its corresponding color-coded screw. Black is on top, then yellow, then green and then red on the bottom. Loosen each screw and loop the exposed wire of each color-coded wire under the appropriately colored screw head and re-tighten the screw.
Plug the black plug back into the test plug and re-secure the clasp. Close the phone line box.
Run the phone line to anywhere you desire. You can staple or attach it to the exterior of the house, go under the house (if it's on a slab) or drill a hole through a wall and silicone seal it. The options are endless. When you're ready, the phone jack comes apart, and there will be four color-coded screws inside that to do the same thing.