Abstract: In a method data are collected about users of mobile telephones which are present within a plurality of defined cells between two specified points in time. For this purpose a list of telephone numbers of mobile telephones is retrieved from a data base, which mobile telephones were located in the defined cells between the two specified points in time. The list of telephone numbers is converted into unique numbers to avoid violation of privacy. Subsequently, the cells are defined in which the housing locations of the users of these mobile telephones are situated. This is effected by sending non-noticeable text messages to mobile telephones on various days at a number of different points in time at which most people are expected to be at home. Based on these text messages the locations of the mobile telephones are established.