This research aims to identify complementary use of e-mail and telephone in organisational context. The first part describes these concepts using information systems theories. The second part describes the study of 61 people of a firm. The number of telephone and email messages measures the level of use. Organisational variables (seniority and power) and alternative media level of use are combined to describe regression models. Results reveal partial substitution phenomenon according to the level of use. Methodological, managerial and research implications conclude this work.