Well, I've finally got the issue resolved.
First I'd like to say that the last few posts have been a bit off-topic from the discussion that originally took place earlier in the thread. This discussion has nothing to do with IMAP syncing, as its specifically addressing active-sync over ports 443 or 80. The topic being covered assumes the following:
1. -You're likely an Admin, and have access to your firewall and Exchange Server.
2. You're forwarding ports 443 (or 80) to your IIS server.
3. You've entered your credentials on the iPhone, and you either can't validate, or you can validate but can't sync afterward.
I reached an Apple representative who was actually very helpful, and he was also familiar with this problem.
This particular client was using a SBS2003 server, which is significant, since the "exchange-oma" virtual directory is automatically created in IIS. For non-SBS servers, its possible that you won't have an "exchange-oma" virtual directory, and if that's the case you will need to create one.
Admins, the good news is that the fix isn't necessarily an Apple fix as much as its an existing Microsoft KBase article: 817379 (
http://support.microsoft.com/kb/817379/en-us ). For my SBS environment, after backing up the existing /exchange-oma virtual directory, I removed it, and created a new one using the /exchange virtual directory as a template.
I followed through the article, and it worked like a charm. Upon doing an iisreset, my client sent me a message from his phone as it almost immediately began syncing.
Good luck to everyone. I'm glad to have this one solved.
FYI my server has a 3rd party certificate installed, but I don't think that's significant to resolving this issue.