PWM whine near earpiece in low signal phone call and loud sound sent to the other end

[dsimic]

I tried recording sound while downloading a large file over 2 G (needed to be slow and bandwidth heavy) and it didn't work. Problem is, when downloading, the transmit power is only very intermittently high and when it pulses high, there is an audible sound (probably from a capacitor charging) that is extremely broadband that limits the ability to pick anything else up.

How about trying to upload a large file under the same network circumstances?  A large file upload should crank the modem's transmit power to the max, and keep it at that level for as long as the upload keeps going.  It should even suffice to run "speedtest-cli --no-download --server <id>" (maybe with the "--single" flag as well) on the phone in a simple "for" loop, so you don't have to search for a fast server that accepts large file uploads.

With the way the sound is configured, I think it should be possible to run the recorder while doing a phone call (which has high upload and high and stable transmit power). I will see how that goes.

It should be possible. As far as I can see, you should pass "-2" together with other relevant flags to Ondrej's audio setup utility, to activate the modem's digital audio interface while enabling the "usual" audio input and output as well, i.e. the earpiece and the microphone.  In other words, that should be a pretty much regular phone call, which could also be placed using the regular dialer application.

Looking at the code, you are right, -2 is what to use. Thank you.

You're welcome.  Thank you for doing all this testing in the first place!