The increase in mobile phone penetration is stimulating a trend towards the use of mobile phones to supplement or even replace traditional telephone surveys. Despite this trend, few studies have systematically compared differences between the two modes. This paper describes a study in which both mobile and fixed phones were used to collect data on a national survey on internet and cultural practices. Findings revealed significant differences between mobile phone respondents and fixed phone respondents in terms of demographic characteristics and responses to some of the substantive items of the survey. In terms of data quality the mobile phone survey proved to be different from the fixed phone survey in two indicators: completion times and percentage of respondents with item omissions. The mobile phone survey was more difficult to implement than the fixed phone survey since much more screening was required to identify working phone numbers; in addition it yielded a lower response rate than the fixed phone survey.