Will OpenGL ES 2.0 cause headaches to iPhone 3G users?1
"When designing your OpenGL ES application, the first question you must answer is whether your application will support OpenGL ES 1.1, OpenGL ES 2.0, or both... Your application should target OpenGL ES 1.1 if you want to support all iPhones and iPod touches."
To put it simple – OpenGL ES 2.0-only apps will not be supported by the iPhone 3G. The question is whether it´s worth changing your iPhone 3G for the iPhone 3G S because of this?
Apple iPhone 3G S Specifications