FYI, I've looked into "gateway" services to send SMS directly and it's pretty expensive! :eek:
If you can do it per these emails ([phone number]@someprovider.tld) you're definitely going to be ahead financially. The problem is when you need to send SMS to a broad range of people and all their various providers. I suppose you have to make them specify which provider they go through. If you already know the email for SMS to the phone, email is certainly the best way to go.