Do my waiters each need their own phone, or can they share one tablet POS system for the restaurant?

Either works. Every device asks for a PIN, so three waiters can share one phone by pressing Lock between them and signing in with their own four numbers, and every round then carries the right name. A phone each is faster on a busy night and costs nothing extra on the add-on. A tablet POS system for a restaurant works the same way at a service station. The Staff, PINs and hours tab in the docs explains Lock and PINs.