Designing viable mobile services requires in-depth understanding of how people deal with their mobile phones on a daily basis. Most studies on the use of mobile phones are based on surveys that ask people how often they think they use mobile applications. While such survey studies have provided numerous insights, they also pose issues of recall, accuracy and common method bias. Fortunately, smartphones enable more direct ways of collecting usage data by installing a background application that logs all user activities. Such smartphone measurement approach has only been applied in a handful of studies, typically limited to Nokia handsets. This paper scrutinizes the reliability of surveybased measures on the perceived use of mobile services by contrasting them with log data obtained in a smartphone measurement study. We analyze the results of a smartphone measurement study carried out in the Netherlands among 129 users of iPhone, Blackberry and Android phones. Users appear moderately accurate in assessing the use of mainstream services like SMS, email and browsing, but not regarding navigation and weather information services. The findings suggest that traditional survey approaches should be complemented with smartphone measurement in order to really understand how users deal with mobile services.