I had a friend that called one in by accident. The cat came in behind him and sat down in the snow about 20' away from him while he was calling coyotes. We didn't know what was going on until we met back up to leave the area and saw the tracks and where he had been sitting. It kind of made our hair stand up on the back of of necks.
I think that the thing with mountain lions is that they are quite curious and will come into a call just to see what is making the noise. While out hunting I have seen them following other hunters and at times have seen where they have followed me down a trail when I hiked out and saw their track on the top of my own.
I had a buddy call a lion out of a mine shaft last year that he filmed.
He's planning to use it in a DVD so I can't give too much away at this time but that lion lived as there was no hunting done during the filming of the DVD. Another buddy called a lion last year, later in the year, with an electronic call in the same area. I suspect it may have been the same lion, not too far from where the mine shaft is.
Neither buddy knows the other and I didn't tell one about the other.
Bring them in on a string. I love this term, if you want to be successful on calling in Elk, try not to just sound like the other caller. We all laugh at each other when we are practicing Elk calling at home or while camping. When I first started calling in Elk, I had no idea what i was doing and it's funny how many I could call in. The biggest Bull that I have called in to date was actually my first. I was making cow calls and screwing it up big time. But it's obvious I didn't screw up...