Employees are increasingly participating in business processes using mobile devices. Often, this is supported by a mobile web application, which accesses various web services in the back-end. The high latency of the mobile network (e.g., EDGE) is perceived by the user each time a web service is called, in addition to the time needed to invoke the service itself. This high latency may lead to low usability, low acceptance rate, and finally compromises the overall process quality. To reduce the latency perceived by the user, we present a caching architecture for web services and an adaptive prefetching algorithm. The key characteristics of our approach are the compatibility with major mobile browsers and the independence of the caching proxy from the front-end application and the back-end services. We evaluate our approach on realistic traces of web service calls in an IT service management scenario. The traces were generated from handling real incidents according to the ITIL (ISO 20000) processes. The results confirm that using our approach, the latency perceived by the user is reduced by 24%.