answering the phone

Some 20 odd years ago my daughter was studying at Plymouth Polytechnic as it was then. A long way from home she would ring home from a call box for a family chat I would ask her for the number she was ringing from and ring her back, as this was cheaper. So I had a short list of numbers she had rung from by my phone at home. I was filling in a form about her Council grant and needed to ask her a question, so I went to the last phone number I had from her and rang it. It rang for about 20 seconds and a girl's voice answered, I said hello Lynn it is your dad here there was a short silence when she asked me who I was and after finding out it really was me she said do you know where this phone is? I said No. Well she said it is in Plymouth Market and I was just walking by and heard it ring!