Is it possible to use the audio part of the cellular module using electron?
I think you could do it but the DATA 
it would take to much data.
I think @frlobo wants to use cellular voice functions, not audio over IP, right?
The provided M2M-SIM will block any voice call for sure, audio over IP would be too expensive.
The only way to solve that issues would be to use a 3rd party SIM.
But no idea if voice is supported by the ublox module and the electron layout/firmware.
@joky Correct! I want to do cellular voice functions with a 3d party sim… But I want to know if the electron will support it. I see some voice labeled pins, but have no idea how to tackle this.
Thanks!
I rather doubt that these pins are broken out on the Electron anywhere
You can have a look at this
https://github.com/spark/electron/blob/master/docs/images/ublox.png
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You are right… I got confused with the I2S3_SD pins, which are labeled Integrated IC Sound Bus. Which I now have no clue what it is! 
Check pin PB5 for reference.
UPDATE:
I see now. Those are the pins available in the micro controller. However they are not connected to the pins in the cel radio/modem. So I2S is actually a sound bus, and although it is available in the celular chip it is not connected to the MCU or to anywhere for that matter… Additionally like @ScruffR Correctly states, the audio part of the Cell IC is not connected or breaked out.
There are two separate I2S (digital audio) busses. The one on the u-blox is what you need to implement a phone-like device, and those pins aren’t broken out on the Electron.
There is an I2S bus on the Electron, connected to the STM32F205 processor, but that’s not for cellular audio; it’s the same digital audio interface that’s on the Photon as well.
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