The Toggle function allows you to switch between two users without allowing them to speak to each other directly. The two users can be either external or internal users. You can also withdraw from the calls and connect the two users with each other. You can also start a conference. 

You are on a call. 

Call the system menu. 

Press the Display key.
The current call is placed "on hold", the user waits. 

Enter the phone number of the second user. 

The second user answers. 

Press the Display key to switch between the two calls. 

When you end a call, the two users are connected with each other (not possible when both users are external).