it would be the last 4 digs of your cell..unles you chnaged the code. but if you dont know the number then look at your cricket bill , it will have the phone number on it, or you will have to go to a cricket store and they can help you with that..
To unlock a cricket phone you should trace the number which may be in the instruction manual that came with the phone. Alternatively you may call you service provide and inquire for it. After you get it insert the four last digits of your number.