Environments such as ski slopes are highly dynamic, as users are constantly moving at high speeds and in different directions, and also many users are foreign tourists, not locals, thus having to roam if they want to access the Web. Unfortunately, this introduces costs that discourage the roaming users to connect. In order to solve this issue, a collaborative wireless access service has been designed and implemented on Android. Simply put, locals to the environment become hotspots on-the-fly thanks to our application, which works on all recent Android smartphones, without requiring to root the smartphone, which shares their mobile data access with the foreigners for the period of time that they are in range whilst legally protecting the sharer from any potential illegal use of the foreigner, e.g., illegal download of copyrighted music through peer-to-peer. We have validated our service with agent-based simulation results, users feedback through an online survey supported by an EU Future Internet testbed and real performance tests on the ski slopes regarding client-to-hotspot connection times, distance and energy consumption.