I have got my LG nexus 4 16GB and hook it up with TMobile SIM card. When I try a test phone call with my wife, it comes with poor quality sound from the small speaker. The call volume is too low. My wife hear the callers voice clearly on the smartphone. It is very difficult to hear what she was saying for me.
Then I go to the setting and setup the volume to maximum level, and use Music Volume EQ app to improve sound quality. However, I am still experiencing the problem and sound is extremely harsh and unbearably loud. I have to put it away from my ear.
It seems to be a audio output bug with Android 4.2.1. To fix the issues and get it working as normal, use volume rocker app to raise the volume setting to the max while in call and then lower it back down.