So this is an interesting issue. I have a corporate email account set up on my phone that decided to stop syncing yesterday... when I go to look at the corporate account under "Accounts" it shows that "sync is OFF", however when I go into the account settings for the corporate account both "Sync email" and "Sync calendar" are checked. I had the same issue with my Hotmail account a little while back and had to remove and re-add it. In today's business world we need to be able to respond to issues on the go. This is supposed to be a "Smartphone," I should not have to remove and re-add an account that I already set up just to get it to sync again, it is a huge inconvenience.
This seems to be a recurring issue on this phone model. I have read several other discussions about this issue, on Verizon and other forums, on these phones.