Gmail users who use the Exchange protocol to sync their contacts, calenders, and push email encountered a nasty surprise upon upgrading their iPhones to iOS 4.0.
Hundreds of people flocked to Twitter in the early morning and afternoon to report that their iPhones could not connect to m.google.com in order to synchronize contacts, calenders, and mail.
As of right now this does not look like an AT&T issue or an Apple issue- many have speculated that the problem was caused by an increased load on Gmail’s servers due to the tens of thousands of people who are upgrading to iOS 4.0. There are also reports (see link below) that there have been sync issues using the iOS 4.0 beta firmware over the last few days.
Some users (http://www.google.com/support/forum/p/gmail/thread?tid=0aea7857b25a174f&hl=en&start=40) have reported that their data is coming in sporadically and have noted that the issue should (we hope) be resolved shortly.