The whole idea of telepathy is actually a meaningless concept which reeks of dualism. What exactly do you mean by telepathy? Sending words to another person separated by space? We do that by speaking. So I guess you mean silently sending words to another person via the electromagnetic field? We do that by texting. Do you not want an external device involved? Well, what on Earth do you mean by external device? Our brain is a device just like any other. In the future perhaps we'll be able to wire up some kind of reciever directly to the neurons so that we don't have to look at anything, but really, what's the difference, and why would it be such an achievement?