NID (Network Interface Device)
The NID is a point where house wires meet telephone wires. It is a smal plastic box, about 4 or 5 inches across, that opens with a screw, which is circled in the image below.
Once you open the NID you will see a number clickable connect points on the right. This is called a "Line INterface Module" and it is circles in red below. There is one of these for each incoing telephone line or dry loop. Some may not be in use at all. If a dry loop or phone line is attached, and the telco has done their job, there should be a tag to show what the phone number for each line is. The telephone companies enter on the left side fro the bottom so the rain won't come in. The house wiring comes into the right side from below.
There is also a test point you can use to test directly to the phone line bypassing house wiring. When you use this to test, you are supposed to disconnect the line as shown in picture 2. above. The test point is circles in image 3 below.
The NID should have line tags to show the phone numbers for each line