I use iPhone 3D Programming by O’Reilly publishing as a reference. It talks about OpenGL ES.
I prefer having the book in front of me, but here is the pre-release online version – http://iphone-3d-programming.labs.oreilly.com/index.html
The only programming I have done on the iPhone (purely as a hobbsyt) has been using OpenGL with C++.
You can create an instance of a C++ class in a Objective C class. In the program’s main Obj C class’s loop I simply make calls to my game’s/program’s main C++ class. Keeps me from having to learn Obj C – for now!
david