So I have been coming to terms with what can and cant be done with dot3 combiners.
You cant use dot combiners on anything but a texture and a constant (or maybe a constant and a vertex color).
You can specifiy two textures for dot3 combining, and this will work in the editor, but on the iPhone itself, will grab one value from one of the textures and use it as a constant.
What this means is that dot3 is useful only for normal mapping and nothing even approaching bump mapping. The difference between normal mapping and bump mapping is that normal mapping replaces the interpolated face normals with normals taken from a texture map, while bump mapping modifies/modulates the interpolated face normals.
For a static mesh, this is not a problem, but for a mesh made up of moving parts (i.e. ones whose face normals are changing), it means that the normals in the normal map will be completely wrong (they point in constant directions).
I am wondering if the limitation of (constant dot3 texture) is something from Unity itself, or is a limitation of the iPhone hardware. An extensive search for information on this turns up nothing. If I can get (texture dot3 texture) happening, I believe I can get something damned close to bump mapping working.