A co-ordinate system like UTM is a ‘map projection’, i.e. a way of projecting the curved surface of the earth onto a flat plane whilst preserving one, but not all, important parameters like distance, area or navigation angles. It was very important when all we had were paper maps for locating and navigating. Digital applications (like Google Earth for example) don’t need to do that, they can visualise the curvature on the fly, in any way you want. The natural coordinates for specifying locations on Earth are of course latitude and longitude linked to a ‘datum’ which specifies the size, and eccentricity of the slightly squashed sphere that is the earth. GPS provides location data in lat/lon, although units can be programmed to convert that to a particular map projection. The only reason I can think of where you would need to adopt a projection is if you were capturing coordinates from a paper map (and not a GPS/Phone), and/or legacy data stored as map projection coordinates. That is very important and there are many utilities which can convert projection coordinates to lat/lon. So the question for me is why you want to use a map projection rather than lat/lon? What is the workflow - from observation to upload that requires coordinates in a map projection? I guess you just want a convenient way of converting the coordinates at data entry?