From what I understand, hearing from experiences of other users, if you have had the phone for less than 3 months, they ask for it back. If you have had it more than 3 months AND you're allowed to cancel, you can keep the phone.

But I remember Vodafone saying that they are selling you the service and the phone is included and as Vodafone don't manufacture the phones themselves they have no control over asking for them back.

Don't take my word for it, that's just how I understand it is, which may be entirely wrong, considering the absolute utter amount of conflicting information being thrown about on the Vodafone eForums at the moment. Really starting to detest Vodafone now.