The hackers have done it again! #Teamwin announced a few days ago on Twitter that they managed to achieve temp-root for the HTC EVO 3D (and the HTC Sensation, since their internals are similar), and they have just released it for public consumption!  User agrabren on XDA has posted the guide to get you started.
The team is working on a couple of tools to help with rooting these devices, they are:
Fre3vo: Fre3vo is a temp-root acquiring tool, allowing users access to a root shell on their HTC EVO 3D and Sensation devices. Â Fre3vo is available for download now.
Fre3dom: Fre3dom is the name of the tool being developed to enable S-OFF on the EVO 3D and Sensation.
Prereqs:
1. You must be able to push files via adb to your device.
2. You must know what a shell is.
Instructions:
1. Download the fre3vo.zip
2. Unzip the fre3vo binary
3. Push the binary via ‘adb push fre3vo /data/local/tmp‘
4. Change the permissions via ‘adb shell chmod 777 /data/local/tmp/fre3vo‘
5. Run the binary via ‘adb shell /data/local/tmp/fre3vo‘
If all goes well, you’ll be kicked back to your computer’s command prompt. (Some may get more messages, but it seems the Sensation buffers the stderr more than the EVO 3D)
run ‘adb shell’ and you should have a ‘#’ prompt instead of ‘%’.
Here is something you all should know before proceeding with messing with your device.
This is temporary root. A reboot will clobber it. Also realize that the system partition is nand-protected (at least on the EVO 3D) so writes won’t stick for long, and there will be issues getting tools like Titanium Backup to work. We are still developing upon this huge stepping stone. We look forward to hearing methods other developers have found to build temp root to either make the device better, or gain perm root even.
So developers, if you have the time and/or the energy, please join these guys in their work to give these two [previously] locked down devices their full S-Off root they deserve! Hit up the source link for more information!
Source: XDA