You can disable/ enable automatic call waiting signalling for a second call during a telephone conversation. 

Disabling the call waiting tone

Press the Talk key. 

Call the system menu. 

Select and confirm the menu item. 

Select and confirm the menu item. 

Press the On-hook key to end the process. 

Enabling the call waiting tone

Press the Talk key. 

Call the system menu. 

Select and confirm the menu item. 

Select and confirm the menu item. 

Press the On-hook key to end the process.