Some Features of the Users' Activities in the Mobile Telephone Network

Daily activity of the users of a mobile-phone network is represented as a sequence of input and output calls and of input and output text messages. Each such sequence corresponds to its spectrum, the distribution of short two-letter sequences of the same type. It is shown that the spectra of any user's sequences are stable, i. e. reproduced daily. Based on this, the notion of a user's strategy is introduced. The number of different strategies appears to be limited, in the sense that the number of user groups with the same strategy is sufficiently small.