Gamestudio + Lite-C would be quite ideal for the iPhone. It only would have to support OpenGL ES.

JIT compilers aren't allowed on the iPhone so the Unity guys had to come up with some way to compile C# to machine code beforehand. Lite-C already compiles to machine code.

Of course such devices don't have much power but this doesn't require a totally different engine design. You just can't have that many polygons and draw calls.