It's easy to invite a third party to a three-way conference
Either as a caller or receiver of the call: You can now set up – and end – a three-way conference easily and smoothly through your telephone keypad. If you are in Switzerland, you can in both situations also initiate international three-way conferences.
Charges
The three-way conference is free of charge for EconomyLINE and MulitLINE ISDN, only the costs of both connections are charged to your account. There is no contract or any formalities.
Setting up a conference