A Google Mobile Help thread might have some signs that Google will be releasing push email for the iPhone.
Before you jump up and down in joy, I am making an assumption on this news from the following details.
In a Google Mobile Help a Googler named Robin marked a user's answer as being correct, when the person said, and I quote:
Google will probably release push email for the iPhone (using an Exchange protocol) in the near future. They have begun supporting push contacts and calendar, and mail is the only data service left to transition. The reason it works on a Blackberry is because all mail goes through the blackberry servers first. This server then pushes the email to your phone.
Now, Googler, Robin, marked the answer as correct. Robin did not comment in the thread to say if the first part or the second part is correct. Clearly, no one would say the second part of her answer is correct. But the first part would be a dream for most Gmail users using the iPhone.
Did Google just validate that they will enable push email support on the iPhone through the Exchange protocol?
Honestly, I wouldn't be surprised to see it soon. They did it for calendar and contacts already, so adding email is the obvious next step.
Forum discussion at Google Mobile Help.