When the interviewer does a prescreening, use this as a way of soliciting more information about the job. If you give specific answer which is not within the requirements of the company, you may find yourself being rejected right away. You should screen your questions to make sure that they don't convey negative thoughts about yourself. If at all possible, avoid a lengthy telephone interview. Once you get the information you need, you can cut the conversation and confirm your interview appointment.
Telephone interview is a risky proposition.
Interviewers are usually cooperative in giving information regarding what the job is all about and its requirements. If you ask them, they can even send you written job descriptions. If you know more about the job and its requirements, this will allow you to align your preparation based on the information you have. The more knowledge you have about the job, the more intelligent preparation you can make. The interest you put into learning about the organization is generally found helpful during the interview.