We use ClickSend to notify our radio station clients that they are OFF-AIR. Speed is essential. We currently use Email to SMS, but may soon move to the SMS API. Perhaps a "whitelist" of pre-approved destination numbers (maybe limited to, say, 300 numbers) could speed up the delay cause by your "approval" process? We need sub- 10 second delivery times. Your current approval process can take an arbitrary (and unacceptable) amount of time.