not sure I understand this. You can lookup which carrier a user uses based on area code and next three digits? what if user ports their number from one carrier to another?
since twilio is so cheap, it's almost always better than email-to-sms. For example, you don't need to figure out which gateway to send to, and google voice users won't be prevented from getting sms.
SMS probably won't wake you up or get your attention if you're busy though. if your phone get push email, then email and SMS are more or less the same - you get push notification buzz and something on the homescreen.