Ipse, both psychiatrists and psychologists can practice psychotherapy. So both could call themselves psychotherapists if they provide that therapy. A psychiatrist is an MD, with a post med school residency in psychiatry. They sometimes provide psychotherapy (for example, here on PC, SecretGarden's therapist is a psychiatrist) but often specialize in diagnosis and prescribing psychotropic meds. A psychologist has a PhD and additional postdoctoral study or clinical internships.

There is an article here on PC about the different types of mental health professionals, which includes more than just psychiatrist and psychologists:
http://www.psychcentral.com/lib/2006...professionals/

For me, the exact degree the person has is less important than their therapeutic approach.