Here are a couple of great ideas to prevent iPhone spam.
* [Spam Free Email (For The iPhone) [on Geek & Mild]][1]
* [TMO Quick Tip – Using Multiple Reply Addresses In Mail || The Mac Observer][2]
[1]: http://seansperte.com/entry/spam_free_email_for_the_iphone/
[2]: http://www.macobserver.com/tip/2006/09/25.1.shtml