When will my unlocked iPhone 4 recognise my SIM?

I have just bought an unlocked iPhone 4 from a guy who lives nearby. It is brand new but was originally on o2 and I need my Vodaphone SIM to work in it. He said it could take up to 48 hours as it is part of the unlocking process but im not too sure whether to believe him. Has anyone else experienced this or have I been ripped off?