I've purchased and installed your plugin successfuly!
I've set it up to work on registration pages, with ClickaTell API. The problem is that it doesn't show anything on my registration form which can be found here: http://www.taxiguider.com/profile/login/ !
Please make sure that your SMS gateway is working correctly and check your SMS gateway account that you have received the message there. Right now we are in vacation. Our office will start from 29th Sept. If this issue remains till that time then I can forward it to the developer after opening our office. Please keep patience.