Go back vs. Come back vs. Get back vs. Be back

It happened a couple months after I moved to the U.S. I was talking to a friend about my plans to return to Brazil. In the middle of our conversation I told him that I intended to come back to Brazil in a few months. Then he told me that I would not come back, I would go back. 

Well, it led me to learn more about these phrases. Both, Go Back and Come Back mean "to return". The diference is that you go back when you return to a place where you started, and you come back when you return to a place where you are now.

Example: 
a) I intend to go back to Brazil in a few months, then I will come back to California. (I'm living in California now, and I'm saying that I want to return to Brazil, and later I'll come back to California)

Now, to make it more interesting, let's bring in two more "backs": Be back and Get Back. Both mean to return too. Be back and Get back have the same meaning, and they can be used in either situation.

Example:
a) I'm going there now, but I'll be back. (I'm here, and I'm going to another place now, but I'll come back later)

b) I'll get back to Brazil. (I intend to go back to Brazil in sometime)

Summarizing the meaning are:
Go back: to return (Portuguese translation: voltar para onde você veio - ir the volta).

Come back: to return (Portuguese translation: retornar para onde estou - vir the volta).

Be back: to return - slang for come back (Portuguese translation: estar de volta).

Get back: to return - the same of go back, but don't specify date. Another means is to retrieve. (Portuguese translation: voltar ou recuperar).