Google much? oh what the hell, that is why we are all here right? No, there are 3 different options for push email, a Microsoft Exchange server (costs an arm and a leg), Mobile Me ($99 a year but gives you a lot more than just email), and Yahoo. Yahoo offers you free IMAP push email for the iPhone. After that you are limited by the (lack of) integration between the server and the client. There is a debate on what true push is. I am just telling you what they are marketed as. huh?
that's only for yahoo though. the thread starter might get confused now. you must point out exactly who get's push and how.