I cannot dial phone calls over the Internet. The FRITZ!Box event log says, "Registration of Internet number failed ... Reason for error: 40x". What can I do?

If you get a busy signal whenever you try to dial a call over the Internet from a telephone connected to FRITZ!Box, and under "System > Event Log" in the FRITZ!Box user interface you see the error message "Registration of Internet number failed ... Reason for error: 40x," then follow the step-by-step instructions described here.

Correct the login information for your Internet telephony provider

1. Open the FRITZ!Box user interface.
2. Click on "Settings".
3. ("Advanced Settings" >) "Telephony" > "Internet Telephony"
4. Click on the "Edit" icon next to the Internet number you want to use to dial outgoing calls.
5. Enter the authentication data exactly as it appears in the information you received from your Internet telephony provider.
6. Click "Apply".

Contact your Internet telephony provider

• Ask your Internet telephony provider whether you have exceeded your Internet telephony budget, or whether there is a technical problem.