When all the telephones in the business district went dead, it was apparent that the failure was in the trunk line, not in the individual lines.

Look in line with the steering column on your left side just below the dashboard line you will see a round button. Press to open your trunk. You can also use your remote to pop open the trunk

No, you should not use a humidifier in a main trunk line that is made out of duct board. This will cause the duct board to rot from the moist.

In a PBX, a trunk card is a connection for a multi use line. Often a trunk card will use a T1 or T3 to provide multiple talk paths on a single connection.

T1 line