Upcoming software update for the HTC EVO 4G will fix calendar & Gmail problems0
However, it appears as though there are still some minor headaches plaguing the handset, but Sprint is on top of it by saying that they're going to push out an update soon. The upcoming software update would place the smartphone to version 3.29.651.5 and will basically pack along fixes that are specific to issues regarding the syncing of multiple Gmail accounts and calendar event edit problems.
Aside from those two explicit items, Sprint doesn't mention any other fixes, but there are other unnamed enhancements to accompany it. Although it's expected to be available shortly, it would probably be best to manually check to see if it has arrived.
HTC EVO 4G Specifications | Review