I've had these interviews before and been asked a short scenario question, such as "what would you do if a customer phoned up but you could not access their account information" etc (that was quite lame sorry but can't think of a better example at the moment!).
If you've done this line of work before, think about difficult calls you've handled (or other people!), also think about when you've gone out of you're way to help someone, how you did it etc whilst adhering to call centre targets.
Think I've waffled but hope this helps.
Good luck x