I try to use texture lookup in vertex shader, but have no success on iDevice (it works on Simulator and windows). I found thishttp://www.mat.ucsb.edu/a.forbes/blog/?p=453. But i had no success on a few devices – iPod 4 and iPad 2. On the Apple docs i found statement, that they doesn’t support texture lookups in vertex shader. But this guy says it works on his device. Actually i’m interested whether someone else managed to get it working?
It is not supported which means whatever works today could stop working with another release so unless you are going to release your software in a controlled environment, I don’t think it is worth the risk.