What is Busy on Busy?
Busy on Busy will help you handle a call when a user is already in a call or conference, or has a call placed on hold.
New or incoming calls can be rejected with a busy signal or forwarded to voice mail. The Busy on Busy will work across your devices.
Enable Busy on Busy in the MoPo
Go to the Teams Admin panel Link
Selec the Voice Menu and go to Calling Policies
In order to turn this on for your entire organization click the Global.
Enable Busy on Busy in PowerShell
Get your settings in PowerShell
Now let set the Global policy to Enable Busy on Busy.
Set-CsTeamsCallingPolicy -Identity global -BusyOnBusyEnabledType Enabled