Using telepathy is not about intruding into someone's head. Our thoughts are private and cannot be stolen by others. But, your thought patterns can be tapped into if you are transmitting signals (consciously or unconsciously) to be intuitively heard.
For telepathy to work there needs to be two participants, a receiver and a sender. Some people are better receivers, while others are better at sending messages.
I knew a woman who would send out mental messages to friends and relatives whenever she wanted to talk to them. You're probably thinking it would have been easier for her to just pick up the phone and call the person she wanted to communicate with. And you would be right. But, she did this because she was living on a tight budget and could not afford a costly phone bill. When she answered the ringing phone she would say something like, "I'm so glad to hear your voice. What a coincidence, I was thinking about you this morning." But, she knew receiving that phone call was no coincidence, because it was she herself who had actually made the first contact, a telepathic communication.
My husband and I, as many couples who have established strong relationships will, often are able to finish each other's sentences. I believe this occurs primarily from knowing one another's habits over the years but do wonder if telepathy plays more than a minor role in this happening.