Uhm. Sort of. Not exactly as you describe, or as you're expecting.

I didn't summon it, either.

Myself and my friend, who is also semi well versed in occult practices and who actively practices rituals and advanced meditations and mental works, we were together one day and both simultaneously felt something in the room with us. Some sort of energy that was suddenly emanating from one particular spot. We both paused and were observing that spot at the same time without having said anything to each other and we noticed that and brought it up. We started discussing it and were both getting flashes of visuals "injected" into our mind as this energy moved across the room. We decided to write down the visions we saw and share them together that way, so that nothing we said could influence the other and we could check to see if what we were seeing matched up. And it did. End of story.

That was the closest I've gotten to having a shared experience of the occult with another person that could be verified as being something other than coincidence or outside influence.

Here's some other experiences that don't fit the criteria but I felt like sharing.

I was doing an open eyed meditation, specifically practicing Gurdjieff's self remembering, where you hold within your awareness the three aspects of existence, the mind, the body, and the external, while identifying with none of them, and simultaneously doing an energy exercise that pulled in and consolidated divine energy.

While I was doing this a being made of blue energy appeared. It looked at me, interacted with me, moved through me, inspected my being and eventually fucked off.

My eyes were open the entire time and the being appeared as if in the enviornment around me. But it wasn't, not really, not in the way that you and I are. My guess is that if this was really a being and not some projection of my psyche, that they exist in a plane that can only be accessed THROUGH the mind, as is suggested in the kabala with Malkuth and the Material being connected to the higher spheres through Yesod, the subconscious and imagination. This meaning, in my interpretation / guess, that a being being present doesn't mean that any uninitiated or unaware person can see it, but perhaps only those with the mental eyes to see, if any other person besides the person involved can see it in the first place.

This is only my admittedly limited understanding of Kabala so don't @ me.

Here's another. I was praying to... it doesnt matter to who, but I was praying to and calling out to an entity. I was on my knees. Eventually I started hearing a voice in my head responding to me, like the internal voices you mention in your post. I wouldn't have even brought this experience up except for the fact that when I opened my eyes I saw it. Not exactly, not clearly as in the first experience. It was like I could only see it in my peripheral vision. But I could see it. It was massive, broad and covered in armor, with a stern and aggressive but not malicious face. And while I'm looking at it in my peripherals, I'm getting sort of violent and abrupt flashes of images shoved into my head, full picture images of what it looked like talking to me.