Back in August HTC stated that they would be unlocking bootloaders on their devices for developers. They kicked things off with the EU version of the Sensation and pledged to unlock the T-Mobile Sensation 4G and the Sprint EVO 3D next. Today they have completed the task by providing the bootloader unlocker for both those devices in US and Euro carriers.
Also, for anyone not sure what we are talking about, unlocking your bootloader does not mean your SIM is unlocked which would allow you to take your device to another carrier. It simply means developers would have access to the operating system. Your carrier will have to unlock your SIM. HTC also goes on to say that unlocked bootloaders will continue to get firmware over the air (FOTA) updates.
Head on over to HTCdev.com if you need to unlock the bootloader on these devices and stay tuned as HTC hopefully unlocks more bootloaders in the near future.