I really want this sign on the doors of the toilets at work!
I am getting fed up of going to use the toilets and waiting for ages outside while I can hear someone having a conversation on their phone inside.
These are accessible toilets and my arthritis makes it painful for me to walk 2 flights of stairs to the next toilets so this makes me grumpy. There are plenty of spaces to sit and make a private call.
Also I think if they are actually (ahem) using the toilet at the same time as their call then that is not very nice.