Hi Jessica, I’ve responded to your email.
The SMS notifications will be sent an international number as well if the country code is included in the phone number (most AirBnB numbers include this, eMail isn’t currently supported by ST)
You can adjust the number of days ahead of checkin to send the SMS in the Manage Property page in the SMS settings section for AirBnB. (this box shows up after a SMS message is entered, highlighted in the image below)
The integration of custom actions with checkin/checkout schedules is planned for a future release.