If you find that you are unable to hear all callers clearly due to low volume, the Set Volume (Incoming) can boost the volume of the incoming call. The volume can be set from 0 (default) to 9 (maximum). Please note that increasing the volume can reduce the quality of the call, so adjustment of this setting may be required after it is set to achieve the correct balance.
Set Volume (Incoming) can be edited in the Delacon portal by visiting Menu > Services > Edit > Set Volume (Incoming)
If you are able to hear callers clearly but they are unable to hear you, please see Set Volume (Outgoing)