This forum is predominantly used to help users with their code or algorithms. The work you require doesn't fall under the forum's remit. If you find some scripts or an API and get stuck on a php-based aspect, by all means post your question.
The more and more you see and read about how other websites are using SMS, the more and more you begin to wonder why you're not. So I'll show you how (in PHP, because it's the only language i know!). Although it is possible to send SMS via e-mail, which I might cover another time.