I am developing an app that will send SMS to a specified recipient at a future time. Does the in-app messaging API allow users to send messages automatically without the user confirming at the time of delivery?
Once the user has given you permission to send an SMS as if from them, you can use the resulting auth token to send an SMS as long as the token is valid. According to http://developer.att.com/support/faqs/oauth-authentication-management-api-faqs, the auth tokens currently handed out don't expire, so yes - you can send the SMS whenever you want. You just have to *securely* hold onto the user's auth token for as long as you need it.