I just recently configured a couple exchange servers so my clients can utilize the Microsoft Exchange Direct Push/Pull feature offered with SP2. It was pretty easy to setup but there were some bumps in the road along the way. The phone that we are using is the 8125 from Cingular, which is a very impressive phone. I activated the DP feature using a Microsoft Technet Article and then configured activesync on my phone to sync with the exchange server.
The only problem is that overtime I tried to sync, I would get the error “A System error has occurred while processing your request. Please try again. If the problem persists, contact your administrator.” I could not figure it out until I came across Microsoft Article 817379. Which explained that I needed to make some configuration changes within IIS on my OWA server. I used method 2 in the document and it worked perfectly. As soon as I made the changes I was able to sync with the exchange server and now am able write and access email from almost anywhere.
Overall, this was fairly painless and I was able to get it all configured in a few minutes. I am pleasently surprised and was preparing myself with hours of configuration and workarounds to get this running. Hopefully, these links provided will help you with getting direct push/pull configured and running.
Addition Reference: I used method 2 this article to configure direct push to synch correctly.