Push Mail Via Yahoo
The iPhone only supports push mail (which notifies you when email arrives without you needing to check your mail) from Yahoo Mail accounts. If you're on the go and want to know when you get an email, setting up Yahoo Mail on the iPhone is easy. Simply add a new account, select Yahoo as the type, and enter your username and password. That's pretty much it.
Push mail using Yahoo works fairly well. The iPhone will alert you when mail arrives, although it may take anywhere from a few seconds to several minutes for Yahoo Mail alerts to reach the iPhone, according to many users. There could be several reasons for the delay, but most likely the iPhone receives alerts via AT&T's EDGE network, which is slower than Wi-Fi access.
The advantage to push mail via Yahoo is that anyone can receive it with no extra cost or effort. The downside is that Yahoo Mail is typically web-based. There are two solutions to this drawback: Pay for enhanced Yahoo Mail, which offers POP access on your computer; or forward an existing email account to your Yahoo address when on the road. Personally, I opt for the latter simply because it's cheaper. Also, just because you receive the notice via Yahoo Mail, that doesn't mean you can't read/respond using another email account set up on your iPhone.