So it seems just like the recently release HTC Thunderbolt the HTC Incredible S too is locking down against the use of custom roms. So it wasn’t just Verizon who wanted the phone locked to it’s default rom but HTC had a lot to do with it as well. The phone features a signature check when flashing recovery images so if you want to install a custom roms, the rom’s signature must match the default rom’s signature! So our best bet is to wait for someone to get us the password locked away in a utopia under the sea guarded by mermen.
Source: Android Police