That SMS script is Just an iframe of someone else's SMS script that KMD is selling at a huge markup, The original sells for $10 here

http://www.websitescripts.org/website-scripts/free-sms-text-messaging-script/prod_6.html

You might find more information if you contact the actual owners of the script. Why anyone would pay an extra 25 bucks to learn how to put something in a iframe, is beyond my comprehension.

Irregardless of all that, I feel that the script is useless because you cannot see more send an sms without knowing the service provider of the recipient. Furthermore, since the 'SMS' is sent using the php sendmail function with no return path, there is no way of knowing that the message was even delivered. If you enter a number, and select the wrong carrier, the message will not be delivered, and you'll never know. I have a lot of numbers in my cell phone directory, but I'll be damned if I know who the service provider is for each one of them.... I suppose I could narrow it down to 6-7 possibilities in half the cases.