Telephone handsets are usually connected to a phone by a cable with
four-pin connectors at each end. I believe these connectors are called
RJ11 (or possibly RJ10). I would like to know the wiring of these
connectors. Specifically, which pins are used for the microphone and
which for the earpiece.

Hi there,

Normal telephone wire has two pairs of wire in it, the green and red
pair, and the yellow and black pair. A standard one-line telephone
actually only uses one pair, usually the green and red pair. The other
pair is a spare and can be used if a second phone line is added to the
house, or for other purposes. On standard four-pin connectors, the
green and red wires use the middle two pins (2 and 3) while the yellow
and black wires use the outer pins (1 and 4).

Telephone's don't work by having one wire go to the earpiece and one
to the microphone, but instead the wires form a circuit, with both
wires going to both pieces. The websites I've linked to below explain
just how they work much better than I could, so I'll leave you with
them.

I hope this answers your question! If you need any further
clarification, please feel free to ask before rating this answer.

Deadlychiapet-ga

Additional links:
Phone-man's Home Phone Wiring Advice Page
http://www.homephonewiring.com/add-jack.html

Howstuffworks "How Telephones Work"
http://www.howstuffworks.com/telephone1.htm

Google search terms used:
telephone wiring

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Request for Answer Clarification by juga-ga on 26 Jan 2003 06:10 PST

Thanks for your answer and the references. It is not quite the answer
I was hoping for but maybe my assumptions were wrong.

I had assumed that, althought the telephone itself was connected to
the network by two wires, the handset had separate cricuits for the
microphone and earpiece. My reason for asking is that I'd like to add
a microphone mute button to a phone by breaking the circuit to the
microphone in the handset cord. I guess it's not going to be as easy
as that! It would cut off the earpiece at the same time.

Unless you have any references that would help further, I'll rate the
answer.

Thanks again,

Julian

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Clarification of Answer by deadlychiapet-ga on 26 Jan 2003 19:51 PST

Hi again,

The information I posted the first time around wasn't quite accurate.
In the simplest possible telephone you could make, it would just be
the two wires inside the phone, but obviously most telephones around
these days are more advanced than that. So I dug a bit deeper, and the
good news is, in a handset the microphone and the earpiece are indeed
connected separately. The microphone uses the green and red inner
wires while the earpiece uses the outer wires. There's a nice picture
of this on the wiretapping page I've included below. This should make
what you want to do quite straightforward since, as you mentioned in
your clarification below, you can just cut off the microphone circuit.

I wanted to be absolutely sure this time, so I grabbed an old phone
handset that was sitting around unused and pulled it apart. It looked
pretty much like the handset on the wiretapping page below (well
except that mine wasn't bugged =)). In my search I also stumbled
across a very extensive telephone page which was useful in finding
your answer, and which you might be interested in.

Regards,
Deadlychiapet-ga

Additional links:
Telephone technology page
http://www.epanorama.net/links/telephone.html

"How Wiretapping works"
http://www.howstuffworks.com/wiretapping3.htm

Just the answer I was looking for. I am delighted!

Julian

Open the handset and see. 

Owain