Many employers conduct telephone interviews as an initial screening, especially for applicants who would have to travel long distances to interview in person. These interviews are usually scheduled in advance.
Unscheduled interviews are also common, however.
When you call to follow up on your resume, you may be asked several questions or be given the opportunity to ask questions. These conversations, though short, are interviews, and you are being evaluated. It's best to consider all conversations with any company employee as an interview. Be as prepared and professional as possible. Practice with a parent or a friend.