tephone installation

How the Wire Gets Into Your Residence
Historically, the telephone companies ran telephone wire above ground, using telephone poles to make wire issues easy to repair, and inconvenient for the general population to access. The wire itself is sources at a telephone company, or telco, central office, and goes through various paths to get into the general vicinity of your home.
Above Ground Wiring
In older neighborhoods (1970s and earlier in the US) and areas that have a high water table, the telephone wiring is most likely going to be above ground. There will be one or more telephone poles in easement areas in the neighborhood that distribute phone service wire pairs to residences using an aerial method of connection. A breakout box is attached to the pole with the main services lines for the area entering in one side, and residential lines running out of the other side. Wires are then ran from the breakout boxes to each neighborhood residence.
Underground Wiring
Most modern neighborhoods have telephone wiring run underground in the United States today. During the neighborhood build out, before building of homes is commenced, breakout boxes are installed in geographically logical points in the neighborhood, and then lines are trenched back to the primary distribution can for your neighborhood, and to each property nearby. Since homes have yet to be built the wiring is merely a stub, and may need to be extended to the home once the house is built at the owner's expense.
The Residential Network Interface Device
Regardless of how the wire is run to your house, the wire terminates on a Network Interface Device, or NID, which is screwed to your home. This device is a gray or tan box about eight inches wide and twelve inches long with a door or doors concealing two compartments. Access to the customer compartment has a simple slot headed screw for customer access. Access to the telco compartment is controlled by the use of a specialized screw head. You can open the customer access compartment of the NID to check your lines for dial tone, check wiring connections inside the NID, and to trace lines coming out of the NID into your home. There is no necessity to open the telco compartment of the NID, since if there is a wiring fault between your house and the central office, you won't be able to repair it. Most NIDs can handle up to 5 different lines.

The telephone line from the pole or breakout box goes into the telco compartment and exits through the customer compartment.
If you have only one telephone line, and there has been no maintenance on your line for a long while, you may have a box which is a predecessor to the NID. This box is simply a plastic or metal cover which is screwed over a telephone wiring box to protect it from the elements and animals. At no cost, the telephone company will come out and replace your old box with a new NID if there is time and available equipment, and you demonstrate a need, such as a method to test for dial tone. Sometimes, phone company technicians will leave this original box in place, and just install a NID between this box and the wiring running to the pole or breakout box. There is no need to be concerned about this, as it usually has negligible effect to your phone service.