I would like to enhance a website in that a user may send an SMS from it for free. Is this possible via a PHP script?
You need an SMS gateway. If you search this website you'll find some.
You can implement a sms sending function to your website with php, but i don't think that you can send sms for free.
If you wish to send/receive sms in your website try the Ozeki NG SMS Gateway's PHP API!
In this website you can find example and detailed information about php developing: http://www.ozekisms.com/index.php?owpn=204&info=php_sms_example
I hope it is useful for you!
I am Creating a local business directory with SMS interactive features to users to know when people visit their Company info. Search offline of the local directory via SMS. Any ideas that will help creating such a websites