Apptoto reads the events on your connected calendar and looks for upcoming appointments that have phone numbers (including area code) in the title or body. e.g. "Fred 9254111212" or "Wilma (925)-411-1212". If it finds a phone number within an appointment, then it will automatically use that to call/sms that person based on your message settings.
Just like phone numbers, you can simply include an email address in the title or body of the appointment. e.g. "Fred - firstname.lastname@example.org".
Apptoto can also pull email addresses and phone numbers from any of your connected address books.