SNS can be used for a lot of things. There are six different subscriber types available at the moment and among them, we use the SMS, email, and push notifications. We use the SMS and Email services to notify admins whenever something goes wrong, but our primary use case is to send push notifications to our mobile devices (customers). The backend engineers work on setting it up on AWS and most of the features like SMS, Email, etc do not need any frontend intervention, but yes for push notifications, the frontend needs to use the SDK to capture and display them.
The pricing of push notifications and email services is quite fair but if you're planning to use it for sending SMS, then it's a bit on the costlier side. Maybe, It is because we don't have proper providers in my country. I would say that going through the AWS pricing page would be the best solution to find the exact pricing for the services you need.