The UTMS buffer can be set to beep when it is 95% full.
To enable this feature, do the following:
Go to PABX3 -> TOOLS -> VT100
Type in 'BEEP 1' followed by ENTER
Please note there must be a space after the word BEEP.
If the feature is already enabled and you wish to disable it, do the following:
Type in 'BEEP 0' followed by ENTER
Please note there must be a space after the word BEEP.