Mysterious Conversation

I was about 13 years old and was on the phone with my best friend at the time. Over the years she has told me frequent stories about her experiences with the supernatural, I feel 100% that she's very sensitive to it. Anyway, we were talking and she was at home, alone. I was in my bedroom but my family was home. After a few minutes of conversing we both heard a click as if someone picked up another phone and began listening to our conversation. We both stopped mid sentence and listened, we then heard what sounded like the crumpling of paper or wrappers and heavy breathing. We couldn't tell if it was male or female. My friend told me to hit the flash button so I did. I could click over and hear the other line, I clicked back over and told her to do the same. She did it and it only sent her directly back to my line, meaning that there was someone else on another phone in her house. She began to panic and cry, which then caused me to do the same. All the while, the 'person' was making a lot of noise, breathing, whispering, crumpling things. I asked her what other phones were in her house and she said that there was a Micky Mouse phone in her mom's bedroom but it was unplugged, but she went and checked anyway. It was in her mom's closet. She then began crying even harder and said 'Kelli, there's a phone in the basement! But I'm not going down there...' We began trying to figure out how anyone would be able to get to her basement, considering the fact that the windows were too small for anyone to crawl through and they were supposedly locked. I told her to go down and check anyway and that nothing would happen. So she began to descend the stairs, but as she reached the last few steps she ran back up saying that she just couldn't do it. She went back into the living room and on the chair across from her was the phone from her basement, she was hysterical. Her mom came home shortly afterwards, she never told her. We talked the next day and she said that it happened again with another one of her friends but not for as long. For me, I do believe this happened as something supernatural, and I'm a huge skeptic. I've never seen anything with my own two eyes, I've only heard things but this was severe and caused me to believe.