The number of households solely equipped with fixed 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 and households with low income. Latest estimations indicate that 4 million households have mobile telephones only, that are about 9 percent (Federal Statistical Office 2009). Experiences from other countries show even higher rates and, in addition, show that the speed at which fixed 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 fixed line phones only.

To shed light on this issue the German Research Foundation was funding a joint research project of the University of Kassel and GESIS in the framework of the Priority Program on Survey Methodology. The project aimed - amongst others - to exercise the characteristics of mobile-only households and to find out more about the methodological background of mobile phone surveys.

In the paper we will focus on the accessibility of individuals for mobile phone surveys. For this, we describe the situation in which people agree to participate in a mobile phone survey. We found that in our survey nearly a half of the interviews were conducted in settings not in the home of the interviewee. We try to find out in which situations people are likely to respond when they are at home and when they are not at home. Besides, the time of the interview will be analysed. From this we hope to learn optimal strategies for contacting people for mobile phone surveys.