Sony DT310 User Manual

The BusinessPhone 50/250 system is equipped to set and
adjust a personal volume.

Use the volume keys to adjust the volume in the earpiece or
the volume of the ringer. The volume keys have an auto
repeat function. Location of volume controls, see section
”Description”.

When you are making a call, the volume keys affect the 
earpiece volume. This is useful when e.g. you enter a 
machinery or a computer room. The earpiece volume can 
be set to 10 different levels.

When the portable is at rest or ringing, the volume keys 
affect the ringer level. Each time you press the key, you will
hear a short ring burst so that you can verify the new volume
immediately. There are 7 ringer levels. At the lowest level, the
ringer is shut off.