On the 4.2.2 ROM too i have the same problem, only when I flash the Beastmode kenel for 4.2.2 the voip is working great
I wipe dalvik cache , cache, system and data before flashing am on hboot 1.39 with the lastest radio 1.01.01.1112. I have flash through TWRP 2.6.3 beta
Can Someone help or tell where to look specifically ??