It upgrades your phone to the latest firmware available on Sony Ericsson without losing any of your user data (contacts, games, pictures etc.). It is also the official way to upgrade your firmware from Sony Ericsson thus it will not void your warranty. The only caveat is that firmware available on Sony Ericsson is always a step behind things like wotan server. For example, the latest wotan firmware for K800 is R1KC001 whereas that on Sony Ericsson is R1JG001.