Pop
It depends whether you are talking about a graduate or experienced hire position. Experienced hire first rounds are always by phone and conducted by a relevant manager from that business area. To prepare just be ready to talk about your work experiences and skills.
Graduate interviews are normally face to face but can be over the phone if distance dictates. The interviewer could be a manager from the business or someone from HR, and to prepare just focus on good examples of typical consulting behaviours like leadership, initiative etc.
Good luck!