Re: No choice
"the use WhatsApp for business is a sackable offence in our company, irrespective if it's on company or personal devices"
Use of WhatsApp on personal devices at work DOES have a use... No client data of course but its good to have an informal channel that coworkers can use to fire some ideas around. That it's not under company control and undocumented is exactly the point - some important things that need to be said might never get said if everything is documented. It allows the watercooler and the 'quiet word' to be extended from the physical office to the virtual.
Plus of course it would be a prime channel to bitch about management