Custom ROM for Samsung ATIV S leaks13
You can use a stock flasher (as opposed to a street flasher, which is something we all want to avoid seeing) and then perform a hard reset. While the CSC is based on Russian, the default language is English. Also, we need to give you the usual warnings. You really need to know what you're doing here or else you could end up with a Windows Phone paperweight, great for keeping papers from flying off your desk,but not really useful as a phone. Also, once you unlock your phone you will probably lose your warranty.
If you do happen to install the ROM, tell us all about it by posting a comment in the box below!
source: XDA via WPCentral