For a large number of applications, mobile devices offer a manifold variety of potentials to improve business processes. However, most projects still fail to be successful with regard to key performance indicators (KPI). There is a growing understanding that human computer interaction is a key factor for the successful use of mobile devices in practice. However, it is still unclear how interfaces can be designed according to the specific needs of a user applying mobile devices in a business context. In this study we show that user experience has a strong impact on efficient human computer interaction. We present the results of a usability study on a mobile tool for IT-Service technicians. The results show that (a) even low experienced users can achieve sufficient task performance with a usable tool and (b) that participants of all experience groups perform better in the field setting compared to the lab.