It's not the sim card you need to unlock, it's the phone! The handset is most probably locked to the Orange network. Almost any little phone accessories shops will do it for you for a fiver. If the phone is a nokia, I have found a website where you can do it yourself for free, I think it's called Nokiafree.com or something.
To get exact answer you need to specify the phone model . Anyway, Most of the GSM Phone can be unlocked using Unlock code . Some brands like Apple iPhones can be unlocked by remote unlock method . If you want to unlock your phone visit http://www.wickedunlock.com/supported-phones/rs11wp7/ . They provide unlock solutions for more than thousands of GSM phones. Also Check out the site http://www.unlocking4free.com/ they provide free unlock codes for some old GSM phones.