Android 4.0 Ice Cream Sandwich, the official version, is still on track for an August release according to the latest company input we’ve seen on Facebook a couple of weeks ago. However, those who are eager to get an OS bump don’t need to wait until then in order to get Android 4.0 in their Thunderbolt.
There’s a leaked ROM available for download with build number 7.00.605.2, containing Android 4.0.3 and HTC Sense 3.6. It also happens to be pre-rooted with “all of the HTC spyware” removed. In order to grab it follow the source link below; it is pretty stable according to the poster as well as the community so it should be pretty close to what your phone will get via the official channels.