I am going to use Game maker 8 to create a prototype of YourCity. The game will have the main functionality but not with the expected graphics. Using this game I will be able to test the concept. I am using pedometers to simulate the mobile phone application.
GameMaker 8 : Using easy to learn drag-and-drop actions, you can create professional looking games within very little time. You can make games with backgrounds, animated graphics, music and sound effects, and even 3D games! And when you've become more experienced, there is a built-in programming language, which gives you the full flexibility of creating games with Game Maker. What is best, is the fact that Game Maker can be used free of charge.