for using the iphone4s with another operator you have to buy the updatable Gevey pro card. then you have to update your gevey according to your carrier by entering manually mnc or one more thing in software of gevey then you can put your another sim with this gevey into phone then hold for a second.
then go to settings then phone section there is a sim application inside that you will see unlock . press that 2-3 times then you will see your phone showing msg of your sim card which you have inside. then wait for few seconds it willl you the signals bars on the phone. ready to operate.
this can use on any iphone4s except canadian fido operator