We present the challenges of building a disconnected geospatial mobile solution and devise five simple rules for the success of your app. This paper will look at the following key issues: Rule 1 Data Storage. Streaming GI data requires good bandwidth, by implementing a caching mechanism the end-user will always have access to the data for a given area. Rule 2 - Use Open Source. Free and Open Source software for GIS has evolved significantly in recent years and in some cases faster than commercial alternatives. The mobile field is a bit different and few experts are using free and open source mobile GIS, despite the good tools that exist. Rule 3 - Use Open Standards. In combination with the use of Open Source products, Open Standards can help future proof the solution. Rule 4 - Simplify User Interfaces. The time of the stylus is gone and users now expect to use their finger for driving the application. Specific attention must be paid to designing simple and clear user interfaces. Rule 5 - Implement Non native Solutions. Should separate solutions be developed for IPhone and Android? Could the answer be instead to actually develop non native solutions reducing development and maintenance costs. Armed with these rules we will look at the challenges on the road ahead to implementing your GI Mobile solution.