Google Calendar and Twilio integrate through Google Apps Script and the Google Calendar API combined with the Twilio Messages API to send SMS reminders to event attendees before meetings, eliminating reliance on email-based calendar notifications that may be missed in busy inboxes. This integration is used by team administrators, event organizers, and business owners who manage meetings in Google Calendar and want to ensure attendees receive a text reminder in addition to the standard Google Calendar email notification. The connection uses a Google Apps Script that runs on a timed trigger, queries the Google Calendar API for upcoming events, looks up attendee phone numbers from a Google Sheet or contact database, and calls the Twilio API to dispatch reminder SMS.
What You Need Before You Start
Open Google Apps Script by navigating to script.google.com, creating a new project, and linking it to your Google Calendar by enabling the Google Calendar Advanced Service under Services in the Apps Script editor, which gives your script access to the CalendarApp and Calendar.Events.list API methods. Store your Twilio Account SID and Auth Token as Apps Script Project Properties by navigating to Project Settings, then Script Properties, adding TWILIO_ACCOUNT_SID, TWILIO_AUTH_TOKEN, and TWILIO_FROM_NUMBER as properties, and retrieving them in your script using PropertiesService.getScriptProperties().getProperty('TWILIO_ACCOUNT_SID'). Create a Google Sheet with columns for Email and Phone that maps each Google Calendar attendee's email address to their mobile phone number in E.164 format, as Google Calendar attendee objects contain email but not phone and you need a lookup table to bridge the two. From Twilio, collect your Account SID, Auth Token, and an SMS-capable phone number registered for A2P 10DLC, and ensure all attendee phone numbers in your Google Sheet are stored in E.164 format with a leading plus sign and country code.
Step-by-Step Integration Guide
Write a Google Apps Script function that uses CalendarApp.getDefaultCalendar().getEvents(startTime, endTime) where startTime is set to new Date() and endTime is set to new Date(Date.now() + 24 * 60 * 60 * 1000) to retrieve all events in the next 24 hours, then for each event call event.getGuestList() to retrieve the attendee array and read each attendee's getEmail() value. For each attendee email, look up the corresponding phone by opening the Google Sheet using SpreadsheetApp.openById(sheetId) and searching the Email column using getValues() to find the matching row, then read the Phone value from the same row. Dispatch the Twilio SMS by making an HTTP POST request from Apps Script using the UrlFetchApp.fetch method with the URL set to https://api.twilio.com/2010-04-01/Accounts/{AccountSid}/Messages.json, the method set to post, the payload set to a URL-encoded string containing To, From, and Body parameters, and the headers set to Authorization using Base64-encoded Account SID and Auth Token via Utilities.base64Encode(accountSid + ':' + authToken). Create a time-driven trigger by calling ScriptApp.newTrigger('sendCalendarReminders').timeBased().everyHours(1).create() from a setup function run once, so the reminder function executes hourly and dispatches SMS for events starting in the next hour.
Common Issues and How to Fix Them
Google Apps Script daily execution quota limits the total number of URL fetch calls to 20,000 per day on a Google Workspace account, which is sufficient for most team calendars but can be exhausted by scripts scanning large organizations with many events and attendees. Add a processed events log in a separate Google Sheet tab that records each combination of event ID and attendee email that has already received an SMS, and skip those combinations in subsequent hourly runs to avoid duplicate sends and reduce unnecessary API calls. The Apps Script UrlFetchApp.fetch call to the Twilio API returns a 400 error when the To phone number is missing from the lookup sheet or is stored without the E.164 plus sign prefix. Add error handling around each UrlFetchApp.fetch call using a try-catch block and log failed SMS attempts to a Google Sheet error log including the event title, attendee email, and error message so you can identify which attendees need phone numbers added to the lookup sheet. Google Apps Script time-driven triggers can silently stop executing when the script throws an uncaught exception during a run, and subsequent hourly runs never fire until the trigger is manually reset. Wrap your entire main function in a try-catch block that sends an email alert to the calendar owner using MailApp.sendEmail when an unhandled exception occurs, ensuring you are notified immediately rather than discovering the issue days later.
How to Get More from This Integration
Extend the integration to Google Contacts by replacing the Google Sheet phone lookup with a call to the Google People API at https://people.googleapis.com/v1/people/{resourceName}?personFields=phoneNumbers using the Apps Script People service to look up attendee phones directly from the attendee's Google Contact record, eliminating the need to maintain a separate phone lookup spreadsheet. Build a multi-tier reminder schedule by running the Apps Script on different triggers: a daily trigger for 24-hour reminders, an hourly trigger for 1-hour reminders, and a 15-minute trigger for immediate pre-meeting alerts, storing the sent reminder tier per event ID and attendee email in the log sheet to prevent sending the same tier twice. Add event-specific SMS content by reading custom fields from the event description in a structured format, such as lines starting with SMS_REMINDER: in the event notes that contain the exact SMS text to send, allowing calendar event creators to customize the reminder message for specific meetings without modifying the Apps Script. Create a post-meeting follow-up by adding a second Apps Script function triggered on a time-based schedule that queries events that ended in the last 30 minutes and sends a Twilio follow-up SMS to each attendee with a thank-you message and a link to submit meeting notes or schedule the next meeting.
Conclusion
Google Calendar and Twilio together ensure every meeting attendee receives an SMS reminder at the right moment without any manual effort, improving meeting attendance rates across your entire organization. Get in touch with Telphi Consulting to build and deploy a Google Calendar Twilio SMS reminder integration for your team.
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