n8n Missed Call SMS Auto-Reply: Twilio + GPT + Slack

Turn missed Twilio calls into instant SMS follow-ups—automatically

This n8n workflow listens for Twilio call status callbacks, detects missed inbound calls, looks up the caller in your Google Sheets customers list, and uses OpenAI (GPT-5.6) to generate a short, context-aware SMS auto-reply—then sends it via Twilio and alerts Slack.

What this workflow does

• Receives a POST webhook from Twilio when a call ends and normalizes the payload while calculating whether the call was missed and whether it occurred within opening hours.
• Filters to missed inbound calls only (busy, no-answer, failed, or canceled) and stops if the caller actually answered.
• Looks up the caller’s phone number in the Google Sheets “Customers” sheet and checks an n8n Data Table to ensure no SMS is sent within the configured quiet period.
• Classifies the caller as an existing customer, a new lead, or after-hours, and proceeds only when a reply should be sent.
• Uses OpenAI (GPT-5.6) to draft a concise SMS reply, then cleans the text and applies an SMS length/segment estimate.
• Sends the SMS via Twilio, upserts a missed_calls record to prevent repeat texts, and posts a tailored notification to a Slack channel.

Use cases

• Sales follow-up: A missed call from a new lead triggers an SMS reply immediately, without spamming during quiet hours.
• Customer service: Missed calls from existing customers get an automated acknowledgment and next-step message.
• After-hours handling: Calls outside opening hours receive an appropriate SMS template and Slack alerts for visibility.

Technical details

• Integrations: Twilio (status callback + SMS), Google Sheets, Slack, and OpenAI (GPT-5.6).
• Workflow logic: if, switch, code (payload normalization, limits/segment estimation), set, no op, plus n8n Data Table upsert/deduping.