The job talk that normally happens in personal texts — the customer asking when you are coming, the technician asking for a gate code. Messages puts it inside Field Promax instead, where the office can see it, the work order can ride along, and it is still there next month.
A shared office inbox — one thread per customer that every administrator can read and answer.
A private direct message between two staff members — office to field, on the record.
Messages is a staff feature, and it needs the customer portal. The chat-bubble icon appears for administrators and service providers only — never for a customer login — and only once the customer portal is switched on for your account. Customers you can message are the ones with portal access; on mobile, the technician's inbox holds staff conversations, while customer threads stay with the office.