I have succeeded in getting normal mapping and specular mapping working on the iPad and iPhone 4! The tangent vectors are calculated on the CPU and interleaved with the vertex coordinates, texture coordinates, and surface normals as VBO objects.
Frame rate is starting to drop below 30fps with one model, so need to work on optimization, texture compression, and LOD algorithms. Perhaps I can also combine the normal map and the specular map together as well.
I learned a lot from these sites while making it work:
The models are from Dexsoft Games which has an excellent indie games license.
Here's an updated teaser image of my work in progress... Next up.. Shadows...