Can I Customise My Android OS to Send Coded Message Through a Phone Call?

Through research I came to know that the mic in our mobile phone takes in frequencies between 300kHz to 3.2MHz and send it during a calling process.

I wish I had a microphone like that! The highest frequency you can pick up with your cell phone mic is about 20KHz.

https://www.researchgate.net/figure/Sensitivity-response-of-mobile-phone-HTC-One-X-using-reference-GRAS-Class-1_fig2_305671983

What actually gets transmitted is less than this. Signal processing in the cell phone extracts the minimum necessary frequency components from the voice spectrum to allow intelligible communication.

Thanks for the the reply

I got that data from this Wikipedia Page

I am also not sure about that

Nowhere in your reference does it suggest an upper frequency limit higher than 22kHz

I am sorry that was not Mhz it was khz

Thanks for pointing out the mistake.

You mean like texting while you're talking?

https://androidforums.com/threads/why-cant-i-text-and-talk-at-the-same-time.256673/

https://discussions.apple.com/thread/5163638

No , i am not looking for that

I am looking for technologies like DTMF.

DTMF technology consists of tones within the audible range. If you press keypad keys during a conversation the recipient will very likely hear them, and you could use add-on hardware to decode them. The phone itself will register and display the numbers, but hacking into that would be a major programming exercise.

https://en.wikipedia.org/wiki/Dual-tone_multi-frequency_signaling

You don't need to modify anything to send a code. "The sky is blue" could be a code for "meet me in St. Louis".

For encryption, you might need to modify the phone.

I'm going to take a guess at what you are trying to accomplish: You want to send a coded message through the audio of a phone call...

Maybe this or something similar is what you are looking for...

https://play.google.com/store/apps/details?id=bit.zeyde.audiomodem&hl=en_US

Yes , exactly

I was looking for this type of apps.

Now i need to know whether is this possible through a phone call at a particular frequency through its transmitting link without making any hardware changes.

I think it should work. The best way to find out is to try it. It's a free app.

Making any hardware change to a phone is nigh impossible, IMO.

I should be able to do it.

But will I be able to reduce the frequency of the input from mic.

I would suggest you contact the developer and explain what you're trying to do.

https://github.com/romanz/amodem/issues