How do you wire a telephone extension?

Can I wire a telephone extension to receive only?

• This will be an extension to a pay phone and we need to prevent users from dialling out. I suppose I could disable the handset keypad but would prefer to fix the wiring.

• Answer:

  You could disable the keypad - but that can be bypassed using a widely available hand held tone dialler costing only a few pounds. It can also be by-passed by tapping out the phone number using the hook-switch, where a number 1 is 1 tap, 2 is 2 taps, 0 is ten taps - nothing other than the existing phone would be required. Your only realistic option is to encase the phone line in some robust trunking and to buy a pay phone.   Nothing that you can do to the wiring will prevent outgoing calls being made, unless you also want to prevent incoming calls at the same time, by cutting all of the wires off or shorting them all to each other.