Can you transfer an o2 simplicity sim card into an iPhone 4?

Can you transfer an o2 simplicity sim card into an iPhone 4?

Yes, if the phone is unlocked or with O2 already.

If it's not unlocked, the original owner can request that it be unlocked through whoever they bought it from; the unlock is actually processed by Apple and sent to the phone via itunes; there are no 'unlock codes' etc. On iphones.