I had a complaint from my one client that their Android phones do not sync anymore to Exchange server via Activesync. I tried to connect to OWA by going to http://server/exchange, and I got the login prompt. Typed in the username / password and it took me to a directory listing. Not what I expected.
To troubleshoot this I compared the settings in IIS for Exchange, ExchWeb and Microsoft-Server-ActiveSync to a known working 2003 server. The settings all seemed perfect, yet it failed to work properly. So eventually I found this article.
The steps I copied from his explanation worked perfectly.
Delete these virtual folders in IIS under Default Web Site:
Start Metabase Explorer, expand the LM key, right click the DS2MB key and select Delete.
Thanks to the author of that article for this tutorial.
That got me half way to the solution. iPhones still could not connect to OMA. After some struggling I decided to check the site with http://www.testexchangeconnectivity.com. And indeed - I got an error on ActiveSync - in specific, FolderSync failed with Exchange ActiveSync returned an HTTP 500 response, which linked to this site. Since I am using Windows 2003 SBS, I had to follow this article instead. Do not skip any steps - follow Method 2 to a T and you should get a clean bill of health on http://www.testexchangeconnectivity.com. iPhone connected just fine.