1. In GMail, create a label name "Send SMS", then create a filter to apply that label to whichever messages you want. For example, every message coming from the email address email@example.com will be applied the "Send SMS" label.
2. Go to Google Apps Script, create a blank project, paste this script into the script editor:
- Every time the Gms_send_sms runs, it will get all email messages which have "Send SMS" label.
- Create an event in the Google Calendar for each message.
- Create an SMS notification for each of those events.
- Remove the label of those messages
3. In the script editor, select Resources menu >> Current project's triggers >> create a trigger to run the Gms_send_sms function every 5 minutes. You will need to grant permissions for the script to access your gmail and calendar apps.