You can connect two subscribers to one another. In doing so, you can connect a currently active call with a call on hold, see To connect two subscribers.

Here you must differentiate between two situations:

After two subscribers have been connected, both of your lines will automatically become inactive.

If you have created a second line (active line), e.g. for an inquiry call, you can connect these two lines by putting the handset on hook or by pressing the Speaker button. If you were called on this line, this connection will be terminated if you put the handset on hook or press the Speaker button. The line previously on hold will once again be active. You can configure this action appropriately (see also 10.2.1 General).

When you directly connect subscribers, you may still charged, even though you are no longer involved in their telephone call. These will only occur on your side if you set up one or both of the connections. If, for example, SubscriberA called you and you called SubscriberB to inquire about something, you will only be charged for the connection to SubscriberB. No costs will be charged if you are called by both SubscriberA and SubscriberB. However, if you have called both subscribers, you will be charged for both connections.