First, we have successfully connected treo 650 from cingular on medianet with exchange server activesync and synced email, calendar, and contacts.
Second, we did have problems.
Running sbs 2003 server, godaddy turbo cert, treo 650 cingular medianet with versamail 3.5.
1 upgraded versamail to 3.5 didn't install eas patch for direct push since phone is with cingular.
2 had error message stating ssl cert wasn't trusted. (we need ssl so unchecking as suggested was not an option and not recommended)
3 purchased $20 a year turbo cert from go daddy root authority valicert which is trusted by palmos. make sure name on cert is same as what you are authenticating with on treo settings. i.e. if it is mail.server.com you want your cert to be mail.server.com listed with godaddy and you want mail.server.com to be the settings in your treo. that way they all match up and are trusted. when you browse to the mail webpage you should not see a dialog popping up about certificate with ie or firefox.
4 encourted problem. still had error message. i noticed by browsing to mail.server.com/exchange that the certificate was saying issued by go daddy which it still does in current working setup but i thought i may see something about valicert which i didn't. i used the palm blazer web browser went to my owa mail.server.com/exchange and got an error message saying invalid certificate do you want to proceed. i called go daddy troubleshooted with sysadmin double checking discovered problem on their end with cert being authenticated by valicert. go daddy called back and problem resolved.
5 tested site again with web browser and didn't give error message about invalid cert. tried to sync with treo 650 to excange server and still no luck. the error message this time was later on in the process and not about ssl. different error message was a good sign.
6 changed login settings for versamail user authenticating to exchange server. test settings and got a success. i needed to add the domain to the username like you do for rpc like DOMAIN\user. everything else is the same. we're ussing ssl so 443 is checked. test the settings and make sure you get a success message.
7 tested an all sync with contacts, email, and calendar from both endpoints treo and outlook and changes showed up. i am getting an error message intermittently, perhaps from bad service where i'm at so i will know later today. most likely, i'm thinking it is an authentication issue with the directory on the server since we are running sbs. it's a different error then i have seen before it's like 1.1 500 http or something. seems more generic to all mobils using activesync. i found a good read about it perhaps here.
http://support.microsoft.com/?kbid=817379 won't know until later for sure with this issue though.
8 everything works!
Final thoughts! it's been fun. I'm glad it is possible to sync the treo 650 from cingular with an exchange server. I hope that in the future it is more simple and easy for others. I registered here hoping to help others. Maybe if we complain palm will notice and do something about homegrown certs. maybe allow us to import the certificate to the treo or add a lookup feature. maybe disable the need for the cert with server. i don't know but i hope it gets more easy!
Good luck
I hope this helps if you have questions feel free to ask.