Question: What is the best way to manage GPS coordinates (latitude and longitude) in django models ?
I know that there is a module called GeoDjango but reading the tutorial seems dedicated to GIS and not simply to manage the latitude and longitude.

I do not care to have convenient interface for the admin because int the application I'm creatin the admin is virtually absent. But instead the application will often comunicate with mobile device such as iPhone that,for example, treat coordinates as double (double typedef CLLocationDegrees).

I would simply like an easy way to manage these data in the model?

Answer: 
They help you write efficient code and solve problems in optimal or near-optimal ways. Without them, you will be reinventing the wheel - not always successfully.

Also, they help you structure your code, so that it can be maintained more easily by encouraging a better design / implementation.
Algorithms and data structures are the basic tools of a programmer. They are as essential as a hammer (or nail gun) to a house framer. They are the tools that solve problems so you don't have to reinvent the solution.

You should understand what they are, why and how they work, and what their shortcomings are. Knowing this will save you a huge amount of time that could be wasted trying to solve a problem that has a solution.