Hi All this is my first post i cant write in italian but i hope my english would be good enough.
My phone also was having problem with heavy echo when in call!
I'm on Cuoco latest Lolipoli ROM
Solution was like lelepanz sayd change in build prop
from :
persist.audio.fluence.voicecall=true
to :
persist.audio.fluence.voicecall=false
BUT also imprtant (didnt worked until i done both!)
DISABLE Google Talk Back in apps manager!
Hope it help someone else also
P.S. Thanks Cuoco for great rom.