The number of households solely equipped with xed line phones has decreased in Germany since 2003. Simultaneously the number of people using mobile phones exclusively has increased; especially among young males living in single households. Latest estimations indicate that 8-12 percent of households have mobile telephones only. Experiences from other countries show even higher rates and, in addition, show that the speed at which xed phone lines are replaced with mobile phones will increase in the future. This change in telephone coverage cannot be ignored in survey practice, since current frames for the selection of households include fi xed line phones only.

To shed light on this issue the German Research Foundation was funding a joint research project of the University of Technology Dresden and GESIS, Mannheim. The project aimed to develop possibilities for combining fixed line and mobile phone surveys. For this, we conducted two surveys one on xed line phones and one on mobile phones with around 1000 interviews each.

In the paper we will explain the outline of the project and present the results of the survey concerning response rates and response behaviour with the help of the disposition codes and further survey indicators. We will show that in contrast to the xed line phone surveys the cooperation rate in the mobile phone survey is much higher. However, it is much more difficult to reach a respondent because many mobile phone numbers do not lead to working phones or the status working/not working is unclear. Hence further research has to be done.