Active sync and autodiscover tests at www.testexchangeconnectivity.com
succeed. AccessMyLAN's activesync tester works from a computer, but the iphone version fails at "Checking version ... FAIL ActiveSync IS NOT available. (Username or Password incorrect.)" I've entered my password many many times, and reset it on the domain controller, so I'm sure that's not the issue.
When I add my Exchange account to my iPhone, I get, "Unable to verify account information."
Any ideas for what I should check in the server configuration?