Some child (or adult with the maturity of a child) is using the phone to make farting noises over the intercom.
There have been several news items over the years about people doing approximately this. Sometimes with hateful comments rather than gross ones.
“A huge meringue with polio who drives everywhere in a beautifully restored Hillman Imp.”
― St. John Morris, The Bizarre Letters of St John Morris
How’s that for Random?
Geoff Pangrac: Even the thread you decided to put it in was random!
I always dreamed of pulling this off in high school (the general prank, not the fart noises), but only was able to figure out the classroom phone numbers, not the intercom code. Still, I pulled off a few prank calls to individual classrooms.
Comics I Don't Understand 
Some child (or adult with the maturity of a child) is using the phone to make farting noises over the intercom.
There have been several news items over the years about people doing approximately this. Sometimes with hateful comments rather than gross ones.
“A huge meringue with polio who drives everywhere in a beautifully restored Hillman Imp.”
― St. John Morris, The Bizarre Letters of St John Morris
How’s that for Random?
Geoff Pangrac: Even the thread you decided to put it in was random!
I always dreamed of pulling this off in high school (the general prank, not the fart noises), but only was able to figure out the classroom phone numbers, not the intercom code. Still, I pulled off a few prank calls to individual classrooms.