The ISDN telephone cannot be reached under the telephone number  .

  1. Check the MSN settings in your ISDN telephone.

    For more detailed information, see the documentation for your telephone.

  2. Make sure that the ISDN telephone is connected to the FON S0 socket of the FRITZ!Box.
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Proceed as follows:

  1. Check whether the telephone is connected to the specified socket   of the FRITZ!Box.
  2. Make sure that all cables are in working order and connected properly.
  3. If possible, try out the telephone at another IP phone socket. ` `
  4. If possible, try out the telephone at another ISDN telephone socket.
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