Although most software engineers have access to various modeling tools, they often use paper and pencil to sketch ideas and to support modeling activities. This is particularly true when they are working in the field, for example gathering requirements from stakeholders. Sketches documented on paper very often need to be re-modeled in order to allow further processing – an error-prone and time-consuming task. The aim of our work is to better integrate these early sketching and modeling activities into the overall software engineering process. We have prototyped FlexiSketch, a mobile application that supports freeform, flexible, in-situ modeling and allows software engineers to annotate their models. Apart from the application and the underlying conceptual solution we also present the results of initial experiments. Those suggest that the tool supports freeform sketching similar to paper and pencil, and that practitioners would be willing to use a tool like FlexiSketch in their daily work.