Yealink SIP-T48G Administrator's Manual page 206

Administrator's Guide for SIP-T2_Series_T4_Series IP Phones
Details of the Configuration Parameter:
features.busy_tone_delay
Description:
Configures the duration time (in seconds) for the busy tone.
When one party releases the call, a busy tone is audible to the other party indicating
that the call connection breaks.
0-0s
3-3s
5-5s
If it is set to 3 (3s), a busy tone is audible for 3 seconds on the IP phone.
Web User Interface:
Features->General Information->Busy Tone Delay (Seconds)
Phone User Interface:
None
To configure busy tone delay via web user interface:
1． Click on Features->General Information.
2． Select the desired value from the pull-down list of Busy Tone Delay (Seconds).
3． Click Confirm to accept the change.
192
Parameter Permitted Values Default
0, 3 or 5 0