@SoCal Tropical Pool Service Sorry for the delay in my response, we've been swamped with getting back to folks and I'm working through notifications in my inbox.
Our recommendation for unregistered businesses is to get an EIN.
Our understanding is that other providers are taking a similar approach as the sole proprietor option is extremely limited and has additional oversight requirements.

We would recommend using RC Team Messaging or potentially other social messaging solutions like WhatsApp.
Happy to discuss this further - feel free to shoot us an email at Community.Support@RingCentral.com