I couldn't find the patch notes on HTC's page but there are some articles around that are saying the patch is to fix "Calendar entries in certain formats force close while editing." I have seen some comments that the bootloader was changed to a different version from 1.30.0000 to version 1.40.0000. I haven't seen anywhere that it is actually unlocked though.
Here is a link to one of the articles:
Sprint EVO 3D getting pre-launch update to fix calendar bug | Android Central