Filling out forms of 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 point to get 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 highest probable user data to be filled in, driven by an initial rule set [1]. We further discuss our implementation and the evaluation results of the algorithm as well as the usability of the prototype.