How to add background music to a call on an Android device?

Question

Android

Given: Android device, mp3 track
Task: you need to add this track as a background to the call. That is, it is necessary that the interlocutor, in addition to my voice, hear the music being played. I ask for your advice, how to do it?
My solutions:
1. Software
But as far as I understand, it is not possible to add background sounds with software to a call on Android. But if suddenly someone knows such software, please tell us about it.
You can go the other way and use a standard call through the telephone network, and use Skype (again Android) or another program that allows you to make calls to mobile numbers. I know that on a PC you can add third-party sounds to Skype. But can this be done somehow on Android?
2. Hard version.
Unsolder the adapter: on the one hand, a 4-pin male jack, on the other, 2 female jacks 4-pin and 3-pin. Dad plugs into the phone, a headset is plugged into a 4-pin mom, a jack from the player is plugged into a 3-pin. The bottom line is to bring the signal from the player into the microphone channel from the headset. Naturally, wiring through diodes, so that there are no waves in the wrong direction. But here I have a question in the following. Will there be problems with exceeding the voltage of the output signal from the player and the allowable input signal of the phone (will there be an excess)? How correct is it to connect the grounds of two devices?
Thank you all for your time!