Try disabling the AV if any on the server.
Check with http://support.microsoft.com/kb/827615
Hope this helps!!

Enable (value 1 )the proactive scanning and background scanning in the registry and under and hkey local machine > system > current cotrol set > services > msexchangeIS > Viruscan.. and start the information store service

Make sure you have SP2 install on the server.

I tried disabling Symantec, same behavior.

In registry I navigated down to MSExchangeIS and no folder for Symantec, so couldnt change setting.

I am 95% we have SP2 how do I check?

Open up Exchange System Manager.  Expand Servers.  Right click on your server and choose properties.
You should see something like the image if you have SP2 installed.

Exchange-Server-Version.jpg

Have you enabled the Calendar sync on the iPhones?  It is not enabled by default.
http://www.google.com/support/mobile/bin/answer.py?hl=en&answer=138740 

HKLM\System\Current Control Set\ServicesMSExchangeIS\Viruscan
BackGround Scanning  -  1
Proactive Scanning -- 1
There won't be any key for Symantec

Yep running SP2.

Yes calendars is enabled on the phone, if i make a calendar appointment on iPhone it will show in Outlook/Exchange, but not other way.

in HKLM\System\Current Control Set\ServicesMSExchangeIS, there is no folder for 'Viruscan'

Thanks for all the help, I am thinking it a simple setting or our SonicWall blocking the port, but 443 (https) is not blocked and it works for contacts (both directions), email (both) and calendars (from phone to server), so I doubt it the router blocking it or nothign would work.

Is there some Active Sync settings to make it push calendar apppointments? or just the 4 check boxes in Mobile services Properties?
ActiveSync.JPG

ooops bad picture, but you get idea

Activesync either works or it does not work - there is no middle ground where it will sync some items and not others.
Have you run a test on https://testexchangeconnectivity.com?  I doubt it will show up anything exciting, but you never know.
Have you tried creating a calendar appointment using OWA on the affected server for a user that doesnot sync?  If not, please try it and see if the appointment reaches the phone and report back.  

I tried the https://testexchangeconnectivity.com, it seems to only test email syncing, and it passed.

Yea i thought Active Sync was all or nothing, but in this case apparantly not.  Mail, contacts is fine but calendars is a fail in only ONE direction, making me pull my hair out.  The bad behavior is the same for all users.  And i know it not my iPhone settings cause i made test account on our other SBS domain and it worked flawlessly.

I actually accessed OWA from safari on my iPhone made some appointments and they did not show up on my iPhone.

ARGGGGGGGGGG

Sure - that would have been too convenient if it had worked ;-)
What flavour / version of iPhones have you got?

variety, but mostly like mine  ..... 3G   3.0 OS

I am thinking the next best thing for me to do is to totally diable our firewall and see if it works, then turn it back on.....does this seem like a good idea.

Check the Massync.dll version on the server and let us know

Massync.dll - file version # is 6.5.7638.1

check the link
https://www.experts-exchange.com/questions/22511262/Activesync-4-2-Error-code-0x85010004-and-Massync-dll-version-6-5-7651-30.html
in this theser is link for MS article which contain the hotfix to upgrade the Massync.dll file

Npatang,

I am scared to apply that, from what i read in article they say dont use this unless it specfic to my problem, and my problem is different, I am not getting an error on syncing, just one aspect of sync isnt working.  

I am scared if I apply this it will mess up other's email that is working, is that a possibility?

Also it is the same version # as the massync.dll file that is on the other SBS server, where if i set up test account my iPhone calender works.

Actually its on you whether you want to update or not, but upgrading shouldn't be cause any issues.

I will probably try it after hours this weekend then, ahh the life of an IT person, have to work when all the others are not.

some more info, every now and then i get these errors:


Error      7/23/2009      4:16:31 PM      Server ActiveSync      None      3005      S-1-5-21-691141774-1188768137-710150079-1747      HERBERT
Unexpected Exchange mailbox Server error: Server: [herbert.Sagetechcorp.local] User: [iPhone@sagetechcorp.com] HTTP status code: [409]. Verify that the Exchange mailbox Server is working correctly.

and these warnings:
Warning      4/27/2009      2:54:05 PM      Server ActiveSync      None      3033      Lynette      HERBERT
Warning      4/27/2009      1:51:57 PM      Server ActiveSync      None      3033      Canyon      HERBERT
The average of the most recent [200] heartbeat intervals used by clients is less than or equal to [540].  Make sure that your firewall configuration is set to work correctly with Exchange ActiveSync and direct push technology. Specifically, make sure that your firewall is configured so that requests to Exchange ActiveSync do not expire before they have the opportunity to be processed.  For more information about how to configure firewall settings when using Exchange ActiveSync, see Microsoft Knowledge Base article 905013, "Enterprise Firewall Configuration for Exchange ActiveSync Direct Push Technology" (http://go.microsoft.com/fwlink/?linkid=3052&kbid=905013).

HERBERT is the SBS server

Please check with KB 905013, surely an issue with firewall

Sigh, set up router according to KB 905013, to no avail.  

Going ot try this next ......http://support.microsoft.com/kb/883380

Can you have a look through this link which suggests possible issues with Host Headers and IP Address aliases.  This is in response the the Event ID 3005 you posted.
http://www.eventid.net/display.asp?eventid=3005&eventno=2656&source=Server%20ActiveSync&phase=1 

Alan,
The description in the link you suggested has HTTP status code: [400], but the event id says 409, I am 100% sure that if they can check with the Router/Firewall the heartbeat Interval that the Event ID is throwing will resolve the issue....

I'll be happy if it is ;-)

We were able to fix the iphone issue. Under share calendar... in outlook we changed the default user from no permission to reviewer, and we were able to synch. But, we realized that everyone in the exec group could view our CEOs calendar which is bad. We changed the default permission back to default user no permission, but execs could still see it!! Normal production users cant see it, but I think certain groups allow the users to see it. I can't figure it out. I know the admins can obviously, but they arnt true admins. How can we fix this?

If you have fixed the iPhone issue, you would be better off closing this question down and opening up a new question in the relevant zones to address the permissions / access problems.