>There is one onbard CALLBACK with VFP 6, (i thinks its a call back): COMRETURNERROR()

This is not a callback at all. It simply instructs your VFP COM server to raise a COM error by populating the COM exception structure and returning control to the calling process.

A callback is a very specific programming term that I think you are trying to use generally. It deals with delegating timing control to a called process, and allowing that process to directly invoke a function inside the caller.

I would venture to say that if you have only programmed in VFP, you have never dealt with callbacks of any kind.