The problem with headsets is you can't hear your own voice. This was solved 5 years ago with the 1st headset monitor.
In what became an epic bodge, the 5 year old headset monitor was finally replaced with a much smaller version. The original design required a large inductor to isolate GSM noise. That was no longer necessary for LTE phones. The original design ganged 2 op amps to drive the speakers in mono. The new design drives the speakers with 2 op amps in stereo.
The original design used cascaded 10x amplifiers in the preamp. The new design uses a single 100x amplifier because 1 op amp had to be bodged for isolating the phone. As in the original design, a voltage follower is required to keep the phone from feeding into the preamp, but the reason wasn't written anywhere. It wasn't to isolate GSM noise.
The original design regulated 12V down to 5V. The new design uses unregulated 4.2V from a battery which lasts 24 hours. The standby current is only 5mA. Peaks get it up to 20mA. It took a lot of bodging to adjust the phone volume. The 5k's double the phone's volume, giving the phone's internal volume control enough room. The only adjustment is the microphone volume.
The decision was made to have the monitor permanently in the headphone line. The headphones were never used for anything else.
There was an idea to use digital mixing in a microcontroller, but this required a lot more parts. The lion kingdom inherited a lot of AD8604's from the day job. These are insane rail to rail 8Mhz op amps.
The headset was a Logitech H111 which had a defect in which the microphone was too short. The decision was made to fix it. Despite having some screws, the microphone assembly is not repairable. After cracking plastic welds & boring out the remanes of the microphone tube, it was ready for a longer tube. The original tube was ordinary pipe with 3 steel wires in it. This was replaced with a longer pipe & 2 steel wires because there was no pipe of suitable guage to fit 3 steel wires in.
After hot gluing it back together, it was a mess with much better sound quality. The tube flops around, but is just rigid enough. Unfortunately, the wind screen was lost. It's completely worthless without the wind screen. A new wind screen was fashioned out of packing foam & hot glue.