-First got to http://tysiphonehelp.com/?page_id=48
(BUT remember ever never upgrade it from itunes directly).
-Put that downloaded file on desktop
-If itunes open hold on the Shift key and click Restore
-Then locate the file that you have saved in desktop(Remember Hold shift key)
Wait for a while
-Click your version either Pc or Mac
-Download it to your desktop
-After your restoration process ends,run Blackra1n which will jailbreak your iphone.
-Blackra1n will now install in your iphone
-Open Blackra1n and install cydia
-then install snow
Probably you should have your iphone updated to 3.1.2 unlocked
NOTE: AGAIN DON'T MISS A STEP AND NEVER UPDATE FROM ITUNES DIRECTLY,REMEMBER TO HOLD SHIFT KEY.GOOD LUCK!!!