My T--who was a specialist in cbt for psychosis told me that often voices start on the inside and go toward the outside as the disease progresses. She also told me about voice hearers--about 5% of the population hears voices but only 1% is sz/psychosis. The main difference is how people react to the voices and whether they are accompanied by delusions. If you are not impaired you are a voice hearer, if you have trouble functioning like having friends or keeping a job or telling reality from not then its sz/psychosis.