How to Make a Handset for Your Mobile Phone.

Resubmit the old guide who had retired to connection problems, of course, this updated guide has eliminated these problems and remains accessible to all users, or nearly so.

Note, the pictures of the old guide those persons using a mono plug, so take them only as a reference.

Material:
An old home phone handset.
A stereo plug 4-pin 3.5 mm or 2.5 mm (depending on your mobile).

Cut the phone connector on the side that connects to the phone and not on the side of the handset. Usually this side is + long.

Peel the flat for about 10 mm and once discovered the 4-wire skinned also this for 2 mm.
Please note these wires are a bit 'special, I recommend tinned before soldering to the connector.

Insert the connector body, it will seem trivial, but often forget ... ...

Solder the wires to the connector contacts that you will find the diagram shown.
Lock the strap clips into the connector, check the connections, check that there are no short circuits between the contacts, at which point you can close the connector.

The work is finished. Plug the earphones in place and you can call us comfortably without ears burn yourself during long phone calls.

Of course now I will indicate the connections:

The telephone cable may have the following colors:

Brown     -microphone
Red        +microphone
White      -earphone
Blue       +earphone

or:

Black     -microphone
Red       +microphone
Green     -earphone
Yellow    +earphone

The jack has these connections:

As you may have noticed I have not indicated where to connect the cable to the connector, this is because there are various models that you list them below. In general you have to connect the microphone and a single channel of earphone, the negatives are usually connected together to ground.

List connection

These are the connection of some models, there are plenty. So I delegate to you to find your model here.
If you do not find your model, you need to disassemble an old headphones to control the connections.