Actually the iPhone does have a true push email client. If you set up a yahoo account, then any email sent to your yahoo account will be pushed to the phone. So If you have any other email accounts like for instance, Gmail. Just go itno your gmail settings on your computer and hit the forward email option. Then have your gmail forwarded to your yahoo account. The result; all your gmail will be pushed to your iPhone theu your yahoo account. Its actually quite awsome!
I must admit though I have been having some issuses with my push mail since the update. My yahoo pushes sometimes and other times I have to check manually. Before the update my yahoo push worked flawlessly! So Im hoping that Apple is busy at work trying to get this problem fixed.