Bacially people will text in via SMS to a shortcode e.g. 84010 then there details need to populate a database from their details are entered into an email auto-responder and SMS auto responder where they receive ongoing communications.
People text in their name and email address and this is sent via the SMS provider as a URL. e.g. [url removed, login to view]
As mentioned this data needs to be stipped and added to the data base so that clients can monitor the campaign and forward ongoing messages to people who have joined.