Simple version (no fancy graphics) of mobile app for iOS + Android with location, server API, Google Maps

Wireframe version (without graphics design) of mobile application for iOS + Android which uses location services, shares location data with server and uses integration with Google Maps services to display locations. Xamarin + MvvmCross solution preferred, but we’ll be happy to hear about other cross-platform techniques (and reasoning). Actually it’s a simple pair of apps - locator and visualizer, which share data through server. Locator app sends single phone’s location to server. Visualizer displays all phones on a map. Locator app: - tracks phone and sends ID + location to server - shows position on map for visual verification (user can see if GPS works correctly) - allows for input of name and text message (status), that are synchronized to server (only one status message; previous one edited and replaced) - plain UI, design is not important Server backend: - RESTful JSON API? maybe some ready-made, open-source solution? - stores: ID, name, location, status text Client app (visualizer): - allows for browsing of tracked phones’ locations on the map (map shows icons and names) - locations are refreshed periodically from the server or changes are pushed by the server (which solution is better, easier to implement?) - initially map is scaled to show 3 nearest phones that are/were tracked - clicking on a tracked phone shows a popup with status text We can divide work into 3 above modules (or maybe even smaller milestones) and release payments gradually. All source code will be thoroughly reviewed before payment. It should keep decent coding standards (for reasons of further maintenance and extensibility). We have our own graphics designer, will polish GUI on our own. We will provide screen mockups and dummy picture files for bitmap graphics elements (to put into the app and we will switch them later). As stated at the beginning, we want simplest solution possible. Further cooperation on extending the app possible if all goes well :)