Filling out forms for web based services on mobile devices is a very time consuming and frustrating task for users because of the limited text input capabilities. This is a critical bottleneck to obtaining a wide acceptance of such services, especially mobile commerce that often requires filling user data. We developed an architecture based on a local proxy on a mobile device and a lightweight algorithm for a comprehensive analysis of forms, which leads to the most probable user data to be filled in, driven by an initial rule set [Chie Noda, John Hamard, Enrico Rukzio, Alexander De Luca, Method and Apparatus for Automatic Form Filling on Mobile Devices, Patent. Publication number EP1777629, Publication date 2007-04-25]. We further discuss our implementation and the evaluation results for the algorithm as well as the usability of the prototype.