You should be able to activate the phone by using any Vodafone sim as tbe phone only recognises the network not the phone number.
If you are wanting to unlock the phone to use on a different network then only the original owner can unlock it.
If you try to jailbreak the phone to unlock it the phone will relock itself to Vodafone as soon as you try to update the iOS.
I recently activated a phone for a friend bu sticking a cheap PAYG sim in the phone which was a sim that had never been used in the phone before.
