Do many people have an "Accompanying Voice" - an equal they converse with? A hypnosis professional told me this is true, so I am asking: is it a fact of psychology that many people have a voice that they talk with "in their head" which talks back to them and helps solve problems? I find that this voice often has a perspective I never had and presents ideas I had not thought of. But it does not just tell me what to do. When I really get in a fix, it backs off and lets me solve the problem "by myself". I am about 50 and it has been there as far back as I can recall.

Is it common to have an "Accompanying Voice" and conversations where both voices appear to have equal standing and independence? Is there research which shows this is something other than a hallucination? (After all, an internal monologue is not a hallucination. Why not have two voices in your mind?) The prevailing idea is that voices are hallucinations, but it seems that they could just be parts of the self. This is a cornerstone of Transpersonal Psychology, which uses a dialog method to help people improve self-awareness and solve inner issues.

Addition: Here is some info from a site about this topic, although it does not address my question directly:


  Because of prevailing attitudes psychiatry and within society as a
  whole, it is important to point out, that there are many people who
  hear voices who can cope with their voices and regard them as a
  positive part of their lives. Neither is it the case that voices have
  always been regarded as a negative experience, throughout history and
  even today there are people who hear voices who find their voices
  inspirational and comforting.
  
  These are facts, that on the face of it are hard to square with the
  negative way that the experience is regarded by psychiatry.


More Addition: Here is a bit about the Voice Dialog technique used in Transpersonal Psychology:


  Voice Dialogue Technique
  The Voice Dialogue technique allows a client
  to gain a deeper sense of inner wisdom and gives them the opportunity
  to identify and examine the voices within. Being armed with this
  powerful knowledge provides a greater resource from which the client
  can draw upon when faced with difficult circumstances. The Voice
  Dialogue guides a client into realizing that there are parts of their
  inner being that propel them, but they are separate from those parts.
  They begin to understand that they are made up of many parts and each
  serves a function and has an energy force that sustains it. With this
  awareness, a client is able to create a balance among all of his
  corresponding and correlating parts and can determine which ones to
  silence and which ones to accentuate.
  
  The "Aware Ego" in Voice Dialogue
  In Voice Dialogue, this heightened
  sense of awareness is referred to as the "aware ego." An aware ego is
  not a trait that one possesses, rather it is a process by which we
  begin to know all of the layers of our consciousness on an intimate
  level. Because there is an negative for every positive, the aware ego
  assumes that you can experience both the beneficial part of your
  consciousness and its opposite. With enough insight into your own
  identity, you can choose freely which one will serve you better, and
  can adjust, alter, and align the parts within to meet your goals for
  healing.


To me, this is about using a process which gets underneath assumptions, especially unconscious ones. The biggest assumption is that we are one singular thing that is consistent and understandable. Not So. But we can become master of ourselves.
From a quick search online I see no reason why you distantiate what you describe from auditory hallucinations:


  a form of hallucination that involves perceiving sounds without
  auditory stimulus.


Given the article you link to, which arguably does address your question (yes, some people report experiencing this), you mainly seem to be concerned that this would unequivocally be considered a mental illness. Your actual question thus seems to be "Is hearing multiple voices always considered a mental illness?".

Judging from the Wikipedia article (and its subheading 'Non-disease associated causes') this is seemingly not the case.


  However, individuals may hear voices without suffering from
  diagnosable mental illness. (Thompson, 2006)


The article by Thompson mentions a study for which unfortunately no source is provided, thus I would take the following with a grain of salt:


  But studies by Dutch researchers that began in the 1990s found that
  some healthy people also regularly hear voices. ... Many of the people
  who contacted them did not find the voices disruptive and had never
  felt the need to consult mental health services. ... The resulting
  studies found that more people might hear voices than psychologists
  had thought, perhaps around 4 percent of the population.


It might, however, set you on the right path to finding the actual studies, or more recent work in regards to how many people report hearing voices not attributed to the self without considering them a mental illness.


Thompson, Andrea (September 15, 2006). "Hearing Voices: Some People Like It". LiveScience.com.