As a newbie this has wasted a lot of my time. If you change the name of your account at google from googlemail.com to gmail.com various google-related programs on the phone will stop working such as sync for contacts, android market, google talk and no doubt a few others. If you have had the phone for a while simply reverting to googlemail should make everything work again. Unfortunately, if you made the change when the phone was new (as I did) some programs may have one name and some the other depending on when you starting using them. I found no way to get at the stored gmail/googlemail.com settings for the problematic programs (anyone?) but deleting the cached data and setting up again worked for some of them. I was beaten by the Market program which I could not shift even by resetting the phone to factory settings (there are lots of complaints about this at google).