Hey,
I just read the job description; I love it. It's actually not thát difficult, which is why I bid the lowest amount possible.
I am aware that I don't have any reviews - I'd be hesitant, at least, to hire such a developer. But I'm a third-year student at Groningen University, studying both Computer Science and Artificial Intelligence (it's not as hard as it sounds - the two studies largely overlap).
Now, for the technical part: after reading the description, I've come up with some ideas on how to handle this. I'm not sure whether you want me to code just the server, or also the phone-bits. If you also want me to write the phone-bits, here's the plan for that:
What I want to do is, I want to use a so-called "platform-agnostic framework". What this is is, basically, something with which you can, once the code is written, run it on most, or all, phone operating systems(Android, iOS, Windows Phone). This is possible because the app uses very little operating system-specific features. What this means for you is that every phone type can be supported, and is supported the moment I finish the project(i.e. you don't have to schedule three times the time it'd normally take, because you need three different apps).
As for the server: that's pretty straightforward. Receive a signal, send a query, receive coordinates, send coordinates. I think I'll use some kind of socket-abstraction, to speed up development.
I'm looking forward to working with you. I really "feel" it, you know?