I have mic problem too, but i even don't hear other side. I'm from Czech Republic, T-Mobile network.
Edit: solved, when even MIUI V6 didn't worked i have reflashed whole my phone using fastboot with files from package aries_images_4.11.7_4.1_cn_929b6ea8d0.tgz. Now it works.
I have tested this rom (1.12.2014) for 24 hours, i had problems with one wifi, connected but without connection and i had some problems with calls, two ougoing calls was deaf (they didn't hear me, i hear them).
To change cpu frequency for Mi2S i made small init script to run from init.d, but something rewrited this values so i used app boot shell.
My script inspired by wajk: http://pastebin.blesmrt.net/pik5xl1gu/vkbhbl/raw...
M1cha: please think about merging data and sdcard partition to one partition like on nexus, kindle and other devices. /sdcard is mounted using some fuse to emulate permissions. I have this on my 8GB kindle fire (otterX) and kindle fire KFSOWI.
It looks like it doesn't protect from unlock in pocket by proximity sensor and calendar sync is broken.
Edit: Wipe cache in recovery to fix calendar sync.
To proximity lock i use https://play.google.com/store/apps/details?id=com.itsme4ucz.screenoff set value of covered sensor to 5 and override...