Some users reported to Apple [AAPL] that their iPhone running iOS 4 was struggling to connect to Exchange servers. This isn’t something we have noticed ourselves here and we use Exchange server for email, contacts, calendar and tasks (separate app). However, Apple has provided a quick update that essentially just changes the idle timeout. Users are reporting that this does indeed fix the problem.
Immediately after updating to iOS 4, some users may notice that Exchange ActiveSync Mail, Contacts, or Calendars do not sync, or sync very slowly. In addition, some Exchange Server administrators may notice their servers running slowly.
Products Affected
iPod touch, iPhone 3G, iPhone 4, iPhone 3GS
Resolution
To work around this issue, users should install a configuration profile from Apple that increases the amount of time the iOS 4 device will wait for the Exchange Server to respond to its sync requests. For best results, the profile should be installed on as many iOS 4 devices at your company as possible.
The update is simple to install and can be found here. Download it or view this page on your iPhone and click the link within the article. Alternatively you can just email the file to yourself and install from the mail app.
You then need to install it and ignore the “profile is not signed” message. Once installed which takes less than a second, just restart your iPhone and you should be good to go.