Phone conversation with potential supervisor?

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I recently emailed a faculty member, informing her I was looking for potential supervisors, and was very much interested in her research. She replies soon after, saying she would be willing to have a phone conservation to discuss my program of study and goals.  
Does this happen often? What should I make of it?  This can't possibly be a interview, because I have yet to submit my application package.

Any tips? How should I prepare for this?