SMS Web Sender is a set of PHP classes which allows SMS sending through existing SMS sites. Currently supports: 1rstwap.com, boltblue.com, fonetastic.com, o2.co.uk, and uk.rbk.com.
if you dont like this script, here
is a link to the search page for SMS on hotscripts...
Also read through this
is a google search for a similar scripts.
It's easy to find similar scripts, all you have to do is search for one on google or hotscripts.