Outlook uses different protocols for email than the HTML used for normal Internet communication. HTML email systems like Yahoo, GMail etc provide email that you can access on your Iphone. In addition, most all service providers have an alternate system that allows you to access your email account via HTML.
Go to your Internet Service provider's home page and look for their email link. That link should be accessable via your iphone. If they don't offer that feature, you would have to set up a second account at one of the HTML sites. I would be surprised if that is necessary though.
Answered Feb 15, 2011
Edited Feb 15, 2011