Adapting a Telephone Handset to a Cell Phone





Introduction: Adapting a Telephone Handset to a Cell Phone

By Bill Reeve (
Adapted for instructables by Mouse (

Disclaimer: The procedure described here may not work for you - that's a risk you have to take. If it doesn't work, or if you break something, it's not my fault - it's part of the adventure's risk. I assume you know how to solder. If you don't, please learn before attempting this procedure.

Introduction: Hooking up an old telephone handset to work with a cell phone is simply a matter of connecting together the correct wires. The goal is to substitute the microphone and speaker in the old telephone's handset for the microphone and speaker in the cell phone's handsfree headset. We will do this by attaching the handsfree headset plug (the metal end that plugs into the cell phone) to the end of the coiled cord attached the old handset. The trick is to identify, and connect together, the correct wires.

Step 1: Materials

You will need:

1. the handset from an old, broken and late-model telephone (please don't destroy an antique rotary phone),

2. the coiled telephone cord that connected the handset to the body of the old phone, and

3. a wired handsfree headset that works with your cell phone.

You will also need a soldering iron and some shrink sleeving.

If your handsfree headset is significantly different from the one used in this example, you might need a method of measuring electrical continuity, like a digital volt meter (DVM) that can measure electrical resistance. If you don't own, or can't borrow and DVM, you can still make this work with a different headset, but you will need to identify the matching wires by inspection or trial-and error.

Step 2: Opening Up the Coiled Cord

First, plug the coiled cord into the handset.

Now that the coiled cord is plugged into the old handset, cut the plastic connector off the exposed end of the coiled cord (the end that would have plugged into the old telephone body). Using a craft knife, remove about an inch of the outer insulation from the cut end of the cord. This should expose four wires.

Two of these wires (usually red and black) connect to the microphone (in the "mouth" and of the handset), and two other wires (usually green and white in the phone handset, but sometimes they are both white in the cord) connect to the speaker (in the "ear" end of the handset).

Step 3: Opening Up the Wired Headset

Cell phone handsfree headsets also contain a microphone and one (or sometimes two) speakers. We are simply going to exchange the microphone and speaker in the old telephone handset for the microphone and one of the speakers in the modern handsfree headset. We are going to do this by cutting the plug off the modern handsfree headset and connecting it to the end of the coiled telephone cord. The trick is to connect together the correct wires.

What we need to do now is identify the wires in the handsfree headset cord. Since each headset is different, there is no one best approach. If your headset is similar to the one Im using in this example, youre in luck. If not, you will have to use this procedure as a guide and figure yours out.

If you can, the next step is to open the microphone enclosure on your handsfree headset. This will show you the wires and their functions. Figure 3 shows a microphone enclosure both "as built" and opened up.

The second image is a close-up of the "opened up" microphone enclosure, showing the identified wires. As in the first image, the speakers are on the left, and the connection to the cell phone is on the right.

Note how the red and green wires that go to the ear bud speakers pass directly through the microphone printed circuit board (PCB). The bare return wire, which is shared by both speakers and the microphone, is connected to a ground plane on the small PCB and passes up to the speakers. The white microphone wire comes in from the right (the side toward the cell phone) and dead ends at the microphone PCB.

So, now we know which wires to use.

Step 4: Identifying Wires: Alternate Method

If you cant open your microphone enclosure, youre going to have to identify the wires using a different method. To help you, the attached image shows what is connected to the separate sections of a typical handsfree headset plug. You can use a DVM to check continuity between the plug sections and the wires.

Step 5: Prepare the Wires for Soldering

Once the handsfree headset wires are identified, cut the handsfree handset cord about 6 inches up from the plug that usually connects to the cell phone. Strip about an inch of the outer insulation away, and you will find the same color-coded wires inside that we saw at the microphone enclosure.

These wires will probably be fine gage, multi-strand and lacquer-insulated. To remove the insulation on these wires, pass the end of each wire through molten solder on the soldering iron tip. Do this a few times for each wire, discarding the solder each time. This will burn off and remove the lacquer and tin the multi-strand conductors.

Before soldering any wires together, you might want to clip them together and test that the system works.

Step 6: Solder It All Together

Now that you have tested and verified that the handset works, all that is left to do is solder the correct wires together. The attached table shows the solder connections for this example. Be sure to put your shrink sleeve on the wires before soldering them together, and be sure to put a larger overall (probably black) shrink sleeve on the cord before you solder any of the individual wires together.

Note that we will only use one of the handsfree speaker wires, and that both the speaker and microphone share the same (bare) return wire.

Step 7: Final Words

You will probably have noticed that there is a button on the microphone enclosure that can be used to pick up, or mute, a call. This normally-open pushbutton shorts between the microphone wire and return. If you want to incorporate a button with this functionality onto your handset, be sure to test it out before drilling any holes in your handset. Some phones need a very low resistance short between the microphone wire and return when the button is pushed, and many coiled cords are too resistive.

In any event, have fun!



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    Linked this to my Instructable...very useful. Thanks.

    Hi, Can anyone help..??

    I want to wire up a speaker mike similar to the ones used by the police in the early 2K or those used with CB radio, to use with my I-phone6.

    Can anyone advise with wiring.

    Thanks, this instructable was very useful for my current project !

    I made it with an old Italian handset and an LG stereo handset.
    I used the original wire (only 3 wires inside), so I identified and use the mic, left (or right) and ground removing and not using one of the speaker.
    My suggestion is: in the lg handset there are 5 wires Ground, Speaker, Mic, Other speaker and another Ground. with the multimeter check the speaker that you want to use and remove the other one. The important thing is make a link and sold together the 2 grounds.


    This is great instructables, I'm attempting to do the same thing but i'd like not to rip off one working handsfree headset, so i'm looking for the 3.5" jack for now with no luck at all. So my question is: because the old fashioned headset is not stereo (is it?!) can i use a 3 pole jack excluding one of the two line out and make it mono instead of stereo?

    I am interested in a characteristic of older (102 to 500 series) ATT and Western Electric phones, namely that when you talk on those phones, you can hear your own voice. I am convinced that the lack of this characteristic contributes to the annoying occurance of people raising their voices and shouting into their cell phones. (If you could hear your own voice, no one would shout into the mouthpiece, since you would be shouting into your own ear!)

    This is annoying in restaurants, and in my living room. The quality of the conversation is definately enhanced by this feedback, and also by the better audio quality of the analog technology of older phones. I thought I might be remembering better than it was, so I bought an old ATT princess phone to see if it sounded as good as I remembered it.

    It does!

    I was very excited to find there are a few "retro" handsets on the market for cell phones. I bought one, but the sound quality is digital, and there is no feedback to the earpiece.

    I was excited again to see that the connecting cord to the handset had the old fashioned modular connector on it, and that it would fit into the ATT handset! So I tried, but no luck. No audio feedback.

    Here's my question: How does the Western Electric 500 series, for example, provide the audio feedback from the mouthpiece to the earpiece? Is the circuitry in the cradle portion of the phone? Can the circuitry or components be isolated so that one could create an adapter that would allow you to plug a cell phone into a 500 series handset, or even the base, and get the audio feedback to the earpiece?


    Hope you can read this OK.

    I have that similar feature (voice feedback) in my old mobile phone. its called private talk. i can turn it on & off. maybe similar circuit can be used.

    Very interesting! What is the model and maker and year of your old mobile phone?


    This is the phone :

    Samsung CDMA Explore SCH5259

    Also I made a mistake. The name of that feature is not Private talk, It's whisper talk.

    Hope this helps.

    In those old phones there was a rather complex audio transformer inside the base that provided the feedback into the earpiece. The same could be accomplished with some electronics.