Land-line telephones connect to a box outside the home or office building called a network interface device. This is the central junction box from which all active telephone cables come. Part of the device is only accessible by the phone company, but there is also an access area for customers. Using this customer access panel, a landline number can be checked to see whether there is a fault in the line.
Locate the network interface device for the phone line. This box is normally located outside the home or office building with other utility boxes and meters.
Use a screwdriver to remove the screw that is labelled "Customer Access" on the front of the network interface device box.
Unplug the phone cord that is currently plugged in to the test jack inside the network interface device box.
Plug a standard corded telephone directly into the open test jack. Pick up the telephone receiver and listen for a dial tone.
Contact the telephone-service provider if there is no dial tone, because the landline is problematic and the issue needs to be handled by the telephone company. If there is a dial tone coming from the phone plugged directly into the test jack on the outside of the building, the problem exists inside the home or office building and can probably be fixed without calling the phone company.
Unplug the telephone from the test jack and reconnect the test jack. Close the network interface device box and use a screwdriver to replace the "Customer Access" screw.
Unplug all the phones in the house or building from the telephone line wall jacks. Then, one at a time, plug the phones back into the wall jacks and listen for a dial tone.
Try using a new telephone cord in each of the telephone jacks. The problem could be caused by a bad telephone cord. Contact the telephone company if there is still an issue.