I've used SmartSIM before on a number of mobiles, you don't need to 'unlock' the phone, the film effectively confuses the phone as to what type of sim is installed. In my case a Orange locked phone was used on O2 and voda quite happily when trying just the sim showed it to be locked.
no risk of "bricking" the phone either...
Link here
DealExtreme: $3.96 i-SmartSim SIM Card Unlock Overlay Attachment for Nokia and Most Other Cell Phones (Yellow)