The caller signals both telephone numbers as his own number. In addition to the number actually assigned by the provider (Network Provided Number), the caller also transmits a telephone number he chose for himself (User Provided Number). The FRITZ!Box displays both numbers in the call list; the first number is the user provided number, and the number in parentheses is the network provided number. If you do not want the FRITZ!Box to accept these calls, set up a call block for the user provided number.

User provided numbers are used by companies with large PBXs (telephone systems) to direct calls to a specific number such as the reception desk or switchboard, for example. Call centers also like to use user provided numbers (for example toll-free telephone numbers) that are completely independent of the number assigned by the provider.

It is often possible to call both numbers back. The network provided number is the telephone number assigned to the telephone line by the telephony provider. It is the "real" telephone number and can always be called back. Unlike the "real" telephone number, though, the user provider number could have been manipulated by the caller since the telephony provider does not check whether the number is correct ("no screening").