Spoke to yet another Yahoo rep today who, after consulting with an Engineer, said, "Oh I just learned that Yahoo small business mail does not support push on the iphone."
So, again, we have mounting proof it is a Yahoo issue about which they seem to be doing nothing....yet some posters on this wall (notably with a Canadian and a French yahoo account) DO have it working.
We could be SURE it is a Yahoo issue but for the fact that everytime someone communicates with them, they get a different answer (which further leads me to believe it IS their issue).
At this point the only real solution is to switch to another mail provider.