Yealink SIP-T2 SERIES Administrator's Manual page 319

Parameters
Description:
Configures the call waiting on code to activate the server-side call waiting feature.
The IP phone will send the call waiting on code to the server when you activate call
waiting feature on the IP phone.
Example:
call_waiting.on_code = *71
Web User Interface:
Features->General Information->Call Waiting On Code
Phone User Interface:
Menu->Features->Call Waiting->On Code
call_waiting.off_code
Description:
Configures the call waiting off code to deactivate the server-side call waiting
feature. The IP phone will send the call waiting off code to the server when you
deactivate call waiting feature on the IP phone.
Example:
call_waiting.off_code = *72
Web User Interface:
Features->General Information->Call Waiting Off Code
Phone User Interface:
Menu->Features->Call Waiting->Off Code
To configure call waiting via web user interface:
1. Click on Features->General Information.
2. Select the desired value from the pull-down list of Call Waiting.
3. (Optional.) Enter the call waiting on code in the Call Waiting On Code field.
4. (Optional.) Enter the call waiting off code in the Call Waiting Off Code field.
Configuring Basic Features
Permitted Values
String within 32 characters
Default
Blank
297