You would like to call a fixed-line number with your mobile phone. A call from your mobile phone to your line in combination with a call from your line to the actual destination number is more economical than a direct call.
Configure the "Call through" function of your FRITZ!Box as follows:
Note: The transmission of your number (Caller ID) must be enabled on your mobile phone. Check your mobile phone and enable this function of necessary.
Proceed as follows to call the desired number from your mobile phone via call through:
You hear an audio signal.
Wait for the acknowledgement tone.
You hear a dial tone.
You hear a ring tone and the connection is established.
In this case you pay for the connection from your mobile phone to your line and for the VoIP connection from your line to the desired number.