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:

1. Select the setting "Call through enabled".
2. In the "Incoming number" field, select the number for which the call through function is to be enabled.
3. Configure in the "Number for outgoing calls" field the Internet telephone number via which the calls to use call through are to be forwarded.
4. Enter a PIN of your choice in the "PIN" field and confirm it.
5. Enable the option "Only accept calls from the following numbers".
6. Enter your mobile phone number in the "1." field

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.

7. Apply the settings by clicking the "Apply" button.

Proceed as follows to call the desired number from your mobile phone via call through:

1. Use your mobile phone to call the number, which has been configured in your FRITZ!Box for which the call through function has been configured.

You hear an audio signal.

2. Now enter on your mobile phone the call through PIN you specified in the "PIN" field.

Wait for the acknowledgement tone.

3. Dial "0" for an outside line. You hear a dial tone.

You hear a dial tone.

4. Dial the number (with local area code) you wish to call. You hear a ring tone and the connection is established.

Dial the number (with local area code) you wish to call. 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.