Users should be able to indicate that they want to receive notifications via SMS.
As User, I can select the channel to receive my notifications by selecting SMS (or email).
I'm assuming that this setting should handle notifications for a given user and shouldn't be on a notification type basis.
I checked all the possibilities for sending notifications, when we use the SMS channel, when we want to get a message to an email address at a specific time, and an option when we don't mark "Use Digest". In all cases, I received correct notifications.