The first part of this paper is an account of the mobile phone coverage in developed countries and a detailed description of the percent of households by type of service in some European countries based on face-to-face-interviews of probability samples. In addition, the history of changes in telephone service in households in from 1996 to 2005 are traced and factors associated with the transformation of household to a mobile-only household are identified. The second part of this paper deals with sampling and nonsampling effects that the increased number of mobile phones has on telephone surveys. The sampling effects, due to coverage problems, might be severe and the approaches to solving these problems may not be straightforward. The nonsampling effects are associated to survey costs and practices, nonresponse issues, and data quality.