When a telephone cable is damaged or an old cable needs extending, running a new cable is usually the best solution to avoid line connectivity problems. However, sometimes splicing the cable makes the most sense; it's easier, faster and less expensive than replacing an existing telephone cable. If you must splice a telephone cable, a splice connector is the safest, easiest and most professional option.
Unplug the telephone cable from its jack. If this is not possible, disconnect the wiring in your network interface device --- the sturdy grey box through which your phone line comes in. This device is usually located in your basement or on an outside wall. Telephone cables contain low-voltage electricity; if plugged in, the cable can give you a shock when an incoming phone call comes in.
Locate the ends of the two cables you intend to splice together. Strip off 1/2 inch of the wire insulation using the wire strippers. If you are using a splice connector that features insulation displacement technology, stripping the wires is unnecessary.
Insert one of the cable ends into the receiving tube of the splice connector. Be sure that the cable is all the way in and hold it steady.
Crimp the splice connector down onto the telephone cable with a crimper or pliers. A splice crimper works best for this, but lineman's pliers will also suffice. When done correctly, you will have a tidy, proper splice inside the splice connector.
Insert the other telephone cable into the other receiving tube, making sure there is only one cable per tube. Hold it steady and crimp as you did in Step 4.
Plug the telephone cable back in to its outlet or reconnect the wires to the network interface device. Hook up your telephone and test it to ensure the splice worked.
Use a connector that contains gel to give the splice extra protection against corrosion.
Since they contain low levels of electricity, never handle live phone wires around moisture.