On busy
If "Call forwarding on busy" is configured on the phone, another incoming call during an active call is not signalled. The call is forwarded to the entered call forwarding destination. Even if call waiting (with or without audible indication) is configured on the phone, another incoming call during an active call is not signalled.
Configuration
Web interface:
•Telephony > Call forwarding > On busy
Phone:
•Settings > Telephony > Call forwarding > On busy
Provisioning: