S 5.79 Protection against call number identification during use of mobile phones

Initiation responsibility: Head of IT, IT Security Officer

Implementation responsibility: User

In the GSM network, the communication partners involved may be provided with the respective telephone numbers. Whether this is actually the case depends on the technical equipment and the configuration of the mobile phones and/or network operators.

On mobile phones, the calling line identity restriction function (for the next and/or all further calls) can be used to prevent your own telephone number being forwarded to the person called. This option can often be found in the menus of the mobile phones in items called "Incognito" or "Anonymous".

The telephone number can also be prevented from being shown continuously by the network operator.

Exchanging mobile phones and SIM cards provides certain protection against the assignment of telephone numbers to certain persons. This way, no permanent assignment between user and telephone number and/or device and user is possible. However, the assignment to a government agency or company, for example, remains.

In addition to the calling line identity presentation, the mobile phone number of a certain person can also be determined using public phone directories, provided that the number is entered there. Therefore, when concluding a mobile phone contract, it should be considered thoroughly whether and/or in which form an entry to public phone directories makes sense. The same is applicable to publishing the telephone number in internal telephone directories and to forwarding it in diverse data collections (forms, competitions, etc.).