hello,
Using Telephone Set is ok but designing a Door Intercom is slight different chapter.
Let say that i have following components:-

Please visit this website it has products of doorintercom which works on 2 wires.

http://www.commco.co.za/kocom.htm

Now i have seen this intercom but its Sound Out put is very low and also iam unable to understand the transistor logic they have used..

I have already made a Door Intercom circuit using LM386 for ampification, KA2410 as a bell IC, this door intercom uses 4 wires, when some some rings the bell intercom uses 18 Volts Dc and during conversation it uses 9 Volts DC.

At Door Side:- It has a condenser Mic, It has a 4 Inch, 8 Ohms , 2 Watt Speaker, It has LM386, 2 watts ,68 ohms resistors and few capacitors. Its a Hand Free type of set with a Push Button for ringing the bell on the intercom connected with this handfree set.


Inside the House:- I have telephone like body ( no dialer or circuit, only body)

Inside the Handset there is a condenser mic , and Carbon Speaker for listen what the user is saying from the door side,

Inside the Body on which the Handset is reseting on the cradle:- There is KA2410, There is a Set Down Transformer ( 500 milli-amperes, 18 Volts and 9 Volts) There is also a LM386. 2200 uf cacpacitor , 25 Volts two capacitors :- 1000 uf , 25 volts, three , 1 amp. diode, one, 5 volts , 5 ohms reisistor one,Transistor A683. . one 2 watt resistor , 68 ohm

Now i want to make this to work on 2 wires and maintain the same voice quality and amlification as it is occuring on 4 wires...( full depulex condition)