My 810 which you 820 is based on no problem as a rule tho' sometimes my cars'
Bluetooth has problems and the caller doesn't hear me but that's a Volvo issue
Been having my 820 for about 5 months, no problem hearing callers or them hearing me. I do notice that before I got Amber the volumn stayed on 30 if I set it there even after a reboot. Now when I turn it on or reboot its only on 13 or so. But when I turn it up it stays at 30 until it shuts down and reboots when it comes back up its at 13 again . Don't know if the volumn rocker affects how people hear you on phone calls, but I know it affects how I hear them.
My mom has an 820, my wife and dad both have 920s. They all sound the same. There are other things that can be a factor, background noise, poor signal, etc.
I had that problem before my AMBER+GDR2 Update.....
Don't know how after receiving and installing the update its working so smooth....
But yes am having Lumia 820, since the first day I used to have this ''speak louder'' issue.... but it has gone now.... Lucky me....