Does anyone have any idea how I could create an SMS service, so that someone can send a text message to a phone number and then a few seconds later they receive a text message back from the server.

So I send a text to my server (or someone elses for that matter) at number 123456789, then the server reads the message, does some process and sends a message back.

Im just wondering if there is some web service that will allow me to do this. I know that its possible to send SMS messages via the web to a phone, but I would like to be able to receive/process messages as well.

Cheers for any pointers,