Vodafone says that they won't do or say anything before I show the invoice of the phone. (I've got the phone from a friend, who doesn't have the papers any more.) They also said, that it might be the case that the phone was locked to one specific SIM card, but since I can't prove that I'm the legal owner of the phone, they can't say more. We haven't tried it with the original SIM card, because the aim was to use the phone with my SIM card.
Thank you for your answer. It's not that important, so don't waste your time with it. I was just curios if kisvukk70 has found a solution or not.