I'm thinking about adding a text-messaging component to one of my web sites, and was wondering if anyone might be able to point me in the right direction.

I've checked out sites like clickatell.com and others that offer services, and I can see how to implement their systems, but what I'm wondering is how do you set up one of those "text your question to 123123" type of services which charge the person's cell account $0.50 / text or so on.

My concern with using clickatell or a similar service is that if I have a rogue account that sends millions of spam text, I don't want to pay for it. If people text me, I want them to pay, and to get enough out of the transaction to cover my costs (development, service fees, etc).

Anyone ever work with such a system?

Thanks