Here's what I did
I have been looking for an answer to this for over a week now. I searched and posted in apple discussions, calls to tech support, searches on MacRumors, Google, etc...
Found this on MacRumors and played around-got it to work.
All you have to do is:
1. Delete your exchange account on your iPhone. (Settings/Mail/Click on account/Delete this account)
2. Locate the SSL certificate for your email server address. Luckily I am the IT guy at work and in a small place so I had it in my documents of all places! You can do a search for .cer files, on your server with exchange installed. It is likely titled something like your organization's name/mail/owa/etc... Attach this file to an email and send it to your iPhone. (I did it from my Gmail account-not my exchange account.)
3. Open the email with the certificate attached and click on the attachment file-then install the certificate on your phone.
4. Go to settings/mail/Add Account/Exchange and enter all your servers information and settings.
That's all! Was easy, however, it pisses me off royally that I had to finally figure this out after scouring the web for an answer. I love 3.0, except for this crap problem.