OK, so I wasn't sure which forum to post this in.
I was calling my grandmother who lives in India last month and the strangest thing ever happened for which I have no explanation and so I was hoping someone could help. Please note that my father lives with me and he was at work at that time (this is important).
I called her on my android phone in the ordinary way using my network provider which is EE. I know that she has an old Nokia brick that she uses.
So I call her and she apparently picks up (it seems like she did) but she is already talking to someone else. Naturally, I thought that she was holding another, different phone in her hand and talking on that to someone else. But then I suddenly hear my FATHER's voice talking back to her. His voice sounds very, very close as if he is also on the same line, on the same phone with me (and with my grandmother). I can hear them both conversing back and forth very clearly and it sounds like they're both on the same line as me. I shout, "Hello!" three times but neither of them can hear me at all.
I then hang up and call my grandmother after 10 minutes and describe to her what happened. She is amazed and perplexed. She tells me that she was speaking to my father on the very same phone 10 minutes ago that she is speaking to me now on and on the same line. So we both understood that I had somehow, accidentally managed to 'hack' in to their line.
What is this called and why did this happen and how did this happen. It was such a weird experience and I would really like to know how this happened. Can someone please explain. Thanks.