The advantage of using a SIM Unlock card is that you do not need to jailbreak your phone with UltraSn0w and there are no changes at all to the firmware on the phone when using this card.
To get the Sim Unlock to work you simply slide it in-between the phone SIM card contacts and the phone and then have the ability to use what ever SIM card you want.
The unlock card does cost $34 though, so you really need to weigh up the advantages with this one.
Technology Update: Daily Updates on newly launched Gadgets, Gizmos, Mobiles, PC's & Laptops, Hacking, Gaming & Emerging Technological Trends.