AASTRA 4225 Vision for MX-ONE (TSE) User Guide EN - Manual (Page 100)

Settings
Dialog 4223 Professional/Dialog 4225 Vision 100
Extra amplification of the handset/headset hearing volume level
For people with impaired hearing, the handset hearing volume level can
be extra amplified. To adjust the level:
Note: A level change also effects a headset connected to the
headset outlet.
Dialog 4223 Professional:
PhoneSet Press (see display).
If
PhoneSet
is not shown, press
more...
until it appears.
Select Press (see display).
Down or Up Press to frame
Set Hearing Level
(see display).
Select Press (see display).
A tone signal is heard, and the display shows the current setting. The
Line 1 key lamp also indicates the current setting;
key lamp off=standard level, key lamp on=increased level.
Change Press to adjust the volume level (see display).
The display shows the new setting. The Line 1 key lamp also indicates
the new setting as described above.
Exit Press to finish setting (see display).
When extra amplification has been selected, the Line 1 key lamp turns
off.