Hi
I have been asked to create a simple "emergency" phone. I have been looking at all kinds of products to put this together. Both for arduino and raspberry pi (or other sbc).
Now that the MRKGSM1400 has launched I see that the library contains something about making voice calls, but what about actually transmitting voice from a microphone and playing back incoming voice via a speaker? Is this possible with this board?
I see that the SARAU201 has some pins for audio as "4-wire I2S digital audio interface" can the MCU use that or do I need extra hardware or is it not possible at all with this arduino?
Any suggestions are welcome

If I can use the MKRGSM1400 does it always require a battery to use the GSM modem? What if I supply it with from a very beefy psu on VIN?
Again, any help would be greatly appreciated