For telephone interviews, there is a range of possibilities for finding samples, according to the requirements of the basic question.

People living in a particular street, a certain town, in all of Germany or even Europe can be interviewed.
The sample might also be drawn according to certain consumption oriented attributes, e.g. on customer data bases.

Partner institutes in language regions where there are no interviewers at our disposition are selected according to whether they use the same survey software. Because in this case an online data exchange can be carried out and the field process can be controlled.