I have created a mobile app for Android and iOS using Phonegap Build. Last year I had nearly finished writing code to use GCM (Google Cloud Messaging) for remote push notifi
If you are already using some mobile AWS SDK, then it's more convenient to use it for SNS too.
That also helps keep your app smaller.
And you're happier as a developer since API calls are somewhat unified.
If your backend is hosted on AWS infrastructure you can use IAM roles for EC2 instances (also Lambdas etc.) to make those call without access key/secret key.