Building AI voice receptionist for HVAC (2-10 tech shops) — want builder input Building a 24/7 voice receptionist for small HVAC shops (owner-operator, 2-10 techs). Job: answer every call, book directly to calendar, route emergencies correctly, stay in lane on pricing/diagnosis. Currently on Retell AI + Cal.com, no CRM layer. Four things I want real experience on, not theory: Feature list beyond booking — what's non-negotiable that I'm not thinking of? Reminder calls/texts before appointment? No-show follow-up? Anything you built that turned out to be the actual differentiator once live with a real client? Follow-ups — is anyone running reminder/no-show sequences natively off Retell + Cal.com, or does that always require bolting on something else? At what point did you need it — client 1, or later? Single Prompt vs Conversational Flow — for straightforward booking flows (not complex support), has anyone actually run both and compared? Where does Single Prompt start breaking down in practice, and at what call complexity? CRM — running lean with just the calendar right now. What actually breaks without a CRM layer, and at what client count did you need one? What's the minimum viable setup people add first? Real numbers/experience over theory appreciated.