Two connections are established when making calls with an IP telephone that is configured for the "LAN/WAN" port. Therefore, you can conduct a maximum of four calls at the same time with IP telephones, and the number of possible calls is reduced.

Example:
If you conduct a call with an IP telephone, six additional calls can be made using the other interfaces.
If two IP telephones are being used to conduct calls, four additional calls can be made using the other interfaces.
If four IP telephones are being used to conduct calls, no additional calls can be conducted using the other interfaces.

You can conduct a maximum of five calls at the same time using cordless telephones that are registered with the FRITZ!Box's DECT base station.

Examples:
If five cordless telephones and an IP telephone are being used to conduct calls, you can conduct one additional call using the other interfaces.
If four cordless telephones and two IP telephones are being used to conduct calls, no more additional calls can be conducted using the other interfaces.

One call can be conducted with each of the analog devices connected to the socket "FON 1" or "FON 2".

A maximum of two calls can be conducted at the same time with ISDN devices connected to the "FON S0" socket. Not every FRITZ!Box model has a "FON S0" socket.

The answering machine and the fax can each accept one call. All other callers hear a busy signal, even if you set up more than one answering machine. You cannot send a fax while receiving a fax, and you cannot receiving a fax while sending one.