John,
Enter your email address in the [Mail Setup Assistant|http://www.apple.com/support/iphone/mailhelper>. It should provide you with the correct settings to be able to send and receive email over EDGE. Don't forget to check out the advanced settings as well if you are still having trouble sending.
If you are having trouble receiving email, make sure no other devices (such as other computers or phones) are trying to access email at the same time as the iPhone, or you might be getting a POP lock. As stated in [this|http://docs.info.apple.com/article.html?artnum=307009] article:
The POP3 mail protocol was designed, and is implemented in many cases, to support one connection at a time. If your ISP is not configured for multiple POP connections, then when two different devices attempt to access the mailbox at the same time, both devices may get locked out, or sometimes they will be prompted to enter the password.
Some steps you can take to prevent this from occurring are not leaving your computer's mail application open, and increasing the interval for auto-checking mail on your computer and iPhone or iPod touch. This setting is available on the device by choosing Settings > Mail > Auto-Check.
Hope this helps,
Jennifer B.