You should never leave a voicemail.
You must always text someone to warn before you call them, according to new dialling etiquette rules.
The Washington Post has published a list of the top 10 modern do's and don'ts when it comes to phone use.
It says if someone doesn't answer at first, don't ring them again straight away...and never ever leave a voicemail.
Other rules include don't use speaker phone in public, and keep chat for emotional issues or arguments, while planning should be done on text only.