I can consistently reach that level on DMT. Check out my thread
here on how I perform my DMT trips. It's most noticeable in the minutes leading up to breakthrough, the time before or right after the last hit. I think a sort of shared consciousness may persist through breakthrough but it's hard to remember the details once you get to that point.
Although this is the easiest way I've been able to reach such a level, it's much more interesting and astonishing on longer lasting psychedelics because you experience it for much longer. Set and setting, as well as dosage, are hugely important. I have a feeling back in the 60s and 70s, people were able to get there much easier because of the higher LSD dosages being taken, and that's why LSD had such a huge impact on people's lives compared to today (not that it doesn't have big impacts on people nowadays, but it certainly isn't causing any cultural revolutions either). I only reached it on LSD when I got it from a very reliable source, the one who laid the crystal, and confirmed my dose of 2 blotters to be 200 mics. Which was an extremely extremely heavy trip. Based on comparisons with that I'd say it takes at least 5-10 hits of your "standard" street LSD to get there, which is rather uncomfortable since the decomposition of street LSD into inactive products contributes to the body load without contributing to the psychedelic dosage. It was also a fairly high dosage of 2ci, something like 30-40mg that got us into the same headspace. I don't recommend that route at all as the side effects were very unpleasant.
It's probably best to try on shrooms, at least 4-5g, try up to 7g if that's not working, but that's the highest dosage I've gone on shrooms. I have an anecdote from a friend who tripped at a Renaissance festival. He had actually just redosed mushrooms after taking some earlier (I'm a little fuzzy on the details, it may have been a mush + LSD combination) and was trancing out in a drum circle watching a fire spinner. After watching that for a seemingly eternal amount of time, he wandered into another drum circle with a lot of other trippers dancing. As they would talk to each other, he would hear two people having a conversation that was actually a conversation he was having with himself in his head just seconds prior. Whenever he tried to talk to someone, they would just be a reflection of his thoughts, saying the things that he intended to say. This parallels my telepathic experiences as well.
I think proper audio/visual/tactile stimulation is essential for trancing out and reaching this level of consciousness. My friend had a drum circle and fire spinners. Whenever I have reached this level on LSD, I usually have either psychedelic rock or some kind of psytrance music playing. There's lots of ways to get the visuals lined up with the music. A computer visualizer is of course an easy way. Or try listening to the music while watching something like Planet Earth on mute. You can actually watch just about anything on mute, as the psychedelic visuals will be enough to help the trance. Cartoons, movies (high budget special effects help), etc, just watch them on mute while blasting psychedelic music. Have you and your trip partner(s) zone out into the audio visual mindfuck, if you need more stimulation, try dancing or touching and massaging each other. Whatever feels right. Later on you can try to break out of the trance and communicate with each other, but if you're tranced out enough, you can't break out of it, and you will find it has very interesting effects on communication.
Now of course this -might- be explicable without the telepathy actually occurring. But to any skeptics, don't try to disprove it until you have first hand experience and know what exactly it is you are trying to disprove. I've come up with a myriad of explanations for it, but having first hand experience of the phenomenon, none of the explanations are really convincing. Maybe that's just how powerful the illusion the mind creates is, or maybe, just maybe, there's something else going on.