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FRITZ!Fon reports "IPEI invalid!"

Registration of FRITZ!Fon fails. The error message "IPEI invalid!" is shown on the telephone's display.

1 Restoring the telephone to its factory settings

  1. Press the "Menu" key on the telephone.
  2. Scroll to "Settings" and press "OK".
  3. "Reset" > "OK" > "OK"

2 Re-registering the telephone