Do i need the original sim card to unlock my iPhone 3gs?

I got an iphone 3gs from my mate, but want to get it unlocked from a store because i'm on O2 not whatever her network was on. Do I require the original sim card in the phone for them to unlock it? Can I leave my O2 sim card in the phone while they unlock it? Any help would be gratefully appreciated.

Hi i'm here to help you. To know the network to which your Iphone 3gs is locked you can use the site http://www.theunlockspot.com/apple-iphone-3gs/rs16wp9/ contact the customer care of this site and tell about your problem. Here they are providing Network lock info service you can pay few dollars and get that service. Using this service you can know the network name to which your iphone 3gs locked. After knowing the network name you can also unlock your iphone 3gs from the same site using remote unlocking service provided by them. You don't need to have the original sim card to unlock your iphone just you can easily unlock it using your o2 sim in it.