NTAC procedure for changing TX/RX level of handset (cordless) worked for severe side-tone volume (echo).

Another annoying aspect of these phone: If you put someone on hold from the DTZ you have to press END to be able to use the navigation key to select the line and THEN press Select to get them back! The DTL-8R-1 was much easier....just press a flashing red line key!!

NTAC says no way around the display timeout.