[otrs] How to deal with calls from new customers?

Hi, What is the recommended way of dealing with calls from new customers? For example, someone calls a help desk who doesn't exist as a 'customer' in OTRS. How can an agent (without admin privileges!) enter in information about a new customer? Right now it won't let me create a new ticket in PhoneView without selecting a valid customer in the From field. Is there something that I'm missing here? Jonathan