My fleet of mobiles are Galaxy S5's. I've toyed over the last couple of years to get the call quality useable, but haven't. Biggest issue is when I speak on the mobile and 3cx app, other party says we sound muffled or in a tunnel. Any suggestions on settings or use? Also could it be an issue with the S5 and does anyone have success with later Galaxy S models? I could look into upgrading the phones if it solves the issue.