90% of all faults reported on residential lines are caused by faulty telephones or faulty extensions.

• Step 1: Unplug all telephones, modems, digital TVs and anything else plugged in to the line. Wait a minimum of 20 minutes then try the telephones one at a time in the main socket.
• Step 2: If this hasn't fixed the problem, unplug everything again. If your main socket has a horizontal line embossed into it with the socket and two screws below it, you have a linebox. Remove the screws and gently pull the bottom part away. Inside is another socket, called the test socket. Plugging a telephone into it will isolate all extensions in the house. If the line is still faulty, it is a line fault and will need an engineer.
• If you don't have a linebox, then your main socket is a master socket and your phone service provider should not hold you accountable for any faulty extensions. The visiting engineer will replace it with linebox and fix the extensions for the price of a callout charge.

• It is worth noting that if your line is ADSL (Broadband) enabled, you must use the micro-filter supplied when trying a telephone in the test socket

  Know what's Your equipment if you are not sure it could prove costly

Unless you have rented extensions from the telephone service provider, the only equipment the telephone service provider has in your house is the main socket and the wiring from it leading outside. There may be a few junction points in addition. Any other extension sockets / wiring are most likely your own property or that of the property owner and your telephone service provider cannot fix it for free. There will be a callout charge plus hourly rate.
In short, it will pay dividends if you are sure before you call whether the fault is on your main socket or an extension.

Another way you can be charge( common sense)you must not do anything to the line that will result in damage (such as smash the socket, cut the wire or install equipment that is not recommended to work with the rented phone line). To put it simply; if the fault is caused by something the customer did to the line, be it accidental damage, sabotage, badly installed extensions or faulty telephone equipment, the company may charge the customer for the engineer visit and repair time as separate