I have a gmail account which before I ever got my iPhone, I had setup to notify me when new mail arrives.
It's easy to do for just about any mail account that will alllow auto-forwarding, or a mail rule to forward incoming email.
In my particular instance, I setup my Gmail account and then went to settings and clicked on "forwarding and POP".
To setup forwarding, select: Forward a copy of incoming mail to and enter your phone number and
@mmode.com (1234567890@mmode.com). Then just make sure that you leave a copy in your inbox, if you want to review the messages later from your PC.
There are variations of exactly what the proper address should be after the @ symbol, but here is a list of ALL of them.
http://www.tinywords.com/mobile.html
Now you can get text notification the moment you receive an email.
One thing to remember- if you get a lot of email, then this might not be the solution for you - depending on your SMS package. Big emails are broken up, resulting in several text messages. I don't get a tremendous amount of email, so I don't have to worry about burning up my 200 messages a month. But some of you might find that even 500 messages isn't nearly enough.
My advise is to test it out for a couple days and see how it goes.
Good Luck!!