Half the phone calls made by a recruiter are to clients. The topic of discussion is an interview attempt, position requirements, offers or negotiating fees. The call may either be cold or warm. A 'cold call' is a call to a client that you have no position with and attempt to get a interview for an applicant or start a rapport by gathering information for future calls.
A 'warm call' is a call to a client with whom you have a position. Don't be too concerned about this type of call. From this point on a call is a call.