If your volume of sending SMS notifications is low (under $10 a month), we don’t charge extra for it. Above that, we charge usage. We currently use Amazon Web Services’ SNS product for sending SMS notifications (aws.amazon.com/sns/sms-pricing) and don’t add anything on top of their pricing.
Click on the link below for more information on SMS notifications.
talkjs.com/docs/Notifications/SMS_Notifications.html