Friend of mine was on the phone with his girlfriend from Hong Kong and she was telling him how she received a phone call from a friend of her father looking for her father earlier in the afternoon. Her father was not home at that time so she quickly took the number down on the caller display and let him know that her father will return the call when he returns.
It slipped her mind until she was sitting at the dinning table with her parents and she realized that she had forgotten to let her father know that his friend was looking for him. When she told him the name and phone number, both her parents looked at each other with a strange look in their faces. Her father asked her if she was certain that THIS person called and left THIS NUMBER. She asked why and her mother said because this friend of your father had passed away half a year ago and this phone number should have been disconnected already. However, her father insisted on calling the number to find out who it really was and of course, the phone was disconnected.
None of them spoke a word of it after the call and she proceed to call my dorm mate in Canada, retelling him what had just happened. (I was in his room when this event took place) My buddy thought she was just playing a practical joke on him so he just laughed it off and said "Oh really? The ghost friend of your father must be bored down there that's why he called" and as soon as he said it, we heard a big bang on his wall and static over the phone with a deep voice asked "WHO ARE YOU?" My friend asked his girlfriend if she heard it she said she didn't hear anything because the phone got cut out for a second. They quickly ended their conversation and I went to bed after because I did not want to get involved with bad spirits. My friend got sick the next day and we never brought it up ever again.