I'm looking for an easy way, which doesn't need Unlocking bootloader or flashing Roms, just like root solution for SE 2011 devices (one click). It's because I currently use my Xperia S for development purposes and can't afford bricking it! please tell me if there is a solution. Thanks!
There's a guide on Rooting Xperia S ICS and GB over at XDAs. Not having any XPeria device, I cannot verify -- but the comments on the thread confirm it working. It does not even require the bootloader to be unlocked.
Requirements for that method:
It also mentions a Root Toolkit.
Alternative: Unlocking the Bootloader
An alternative method involves the SDK, and is described at AndroidPit (German; Google Translate 2 English here). this method, however, involves unlocking the bootloader -- so be aware of Sony's harsh politics when it comes to warranty in this case.
Ok, at last, the mighty user of XDA, Bin4ary, has released a very nice and easy toolkit to root ICS JB roms of most sony phones, including Xperia S.
I used the tool and easily rooted my phone. Very fast and painless. No need to flash or unlock bootloader or anything.
If you are also interested, this is the page on XDA: