I think the phone-a-friend possibility is a lot more interesting because it does force the candidate to verbalize the problem and interpret verbal feedback. If

I think the phone-a-friend possibility is a lot more interesting because it does force the candidate to verbalize the problem and interpret verbal feedback. If you make them do it in front of you, you'll also get to see how they interact with other people under pressure and also how their friend treats their asking of the question will be revealing as well.