Serial communication with cell phones

Hackaday alum [Will O'Brien] has been doing some cellphone integration work. He recently picked up some Motorola c168i cellphones from eBay. It turns out there is a serial port that uses TTL communication with a standard head-phone jack as an interface. [Will] soldered up a connector and used a USB to FTDI cable to interface with the phone. To his surprise he was able to read off the stored text messages even though they were PIN protected in the phone’s operating system. The messages on these units were trivial but this is another example of the importance of clearing your data before discarding your devices.


  1. Willegek says:

    This is a perfect platform to connect to a micro and listen to incoming texts. Then based on the incoming texts an action could be performed, starting/unlocking a car. And it could only react to a certain phone number so you dont have to worry about some bozo dialing a wrong number and leaving your car running all day long.

  2. Anon says:

    I quite like the idea of people being able to start my car by phoning me up!

    “Hey you coming to Joey’s house? I already started your car ;)”

  3. Robby says:

    So forensically, could this be used to recover deleted messages for say some kind of sexting investigation?

    What do you guys think?

  4. michael says:

    Hey this is cool. I love that the Audio port is TTL. We are working on a universal way to do this for Open smart phones. What we are using now is an op-amp to translate 1.2v of the droid to 5v. Would love to get some help finding a good mosfet circuit to do 1.2v level translation.

  5. Michiel says:

    A few years back I did the smame with a old Sony phone. I could make calls by sending AT commands with USART without the use of a MAX232… :)

  6. Addictronics says:

    @ robby, no not from my experience.

    I have been working on a high altitude UAV glider for quite some time now, unfortunately I’ve had to stop due to short funds. This is the exact phone that I used for ground communication (under 10kft)

  7. Inventorjack says:

    @Addictronics: You mean you’ve had to pause for awhile, right? It seems to me that once you’re addicted to electronics/technology projects, it’s really hard to actually quit, even if funds run short for awhile ;)

    Fun-looking project, btw.

  8. Addictronics says:


    Exactly. :) A hiatus more than a true cease in production. Also every time I work on it I find something new that has come out that would work better than what I have. The only think I don’t think that I will ever be replacing is the GPS since it was made before the >60,000 ft ban several years ago, so it will work up to my intended 100,000 ft.

  9. Paul Potter says:

    I’m so giving this a go.

  10. CloudHackIX says:

    @Robby: No, you see exactly the same pieces of memory as the normal phone interface sees, there’s no hidden log of messages.

    I bought one these as an emergency phone because it was the cheapest option ($20 for the phone, $15 for minutes, $10 mail-in rebate after) and later saw this online:

    After toying with from a terminal and the FTDI USB ttl break-out cable, I found it quite annoying to deal with. The phone’s CPU is rather challenged w/ normal moment-to-moment issues and often misses incoming characters, which means that a microcontroller would have to do a LOT of feed-back checking to ensure it’s commands actually go through. (As I recall, I know you can have it just spit out when a phone call or text arrives, but I don’t think it’ll spit out the body of the text message, only the sender)

    For anyone interested in working with one of these, be sure to read through the AT command list for the G24 which is what you’re really talking to:

  11. CloudHackIX says:

    I should also mention I found those PDFs from this forum post:

  12. I have been doing for almost 4 years.
    I used some old Siemens cellphones like the A56 and my old M55.
    what I did was use a cable RS232 to TTL.
    to normalize the signals I used an HEX inverter between the cable and the phone.
    what I did was a application to execute shell commands sent on SMS.
    To read the SMS from the cellphone I used GAMMU to talk with the phone and my main code was made on TCL and all that under Linux.
    It was a small University project.
    If you find it interesting or need more info please feel free to contact me

  13. Haku says:

    The Nokia 6100 also has a serial comms which can be used to sending/receiving texts and making calls. Nokia even provide an AT command set:

    More info on using a Picaxe chip to communicate with the Nokia 6100 at

  14. jeditalian says:

    siemens M55 (M56 in U?S) was a great phone. my brother and i both had one in high school and i bought a couple more on ebay and kept Franken-phone-ing them together every time one of them broke ( we were really rough on them) i lost one for a few months and when i found it in the ground, with mud all over its chips..
    it didnt work. so i had to franken-phone it together to recover my data.
    i use to text all day long, never having to look at what i was typing. i wish someone would make a phone that cool with modern-technology (although COLOR LCD was top-of the line back then)
    i didn have any trouble getting it to run all kinds of java programs. nowadays you have to use the master key and operator code. but the lights, they were fun to bust out at a club, or a concert, or when you’re in the dark and someone is rollin’

  15. jason says:

    Open GPS Tracker uses this phone for same purposes.

  16. therian says:

    Most windows mobile phones have hidden com port on usb pins, and it very handy as pocket terminal with full physical keyboard

  17. Manik says:

    Nice work man..Maybe you me? I need a ismi imsi sniffer?

  18. Coolins says:

    It is true, data pin protections can only work in the phone system The pin software only disables opening the message by asking a pin before opening a message but the message itself is not encrypted.

  19. Can this phone be used for data connections and not just SMS activities?

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