Who contacts Christine by special phone in Part 1: Today? How does she know this person?

A phone in Christine's handbag rings and she answers with some trepidation. The voice on the other end is vaguely familiar. A man introduces himself as Dr. Nash, a doctor who has been working with her without Ben's knowledge in hopes of helping her recover her memory. Dr. Nash asks Christine if he can come by and pick her up, and Christine agrees.