Hello,

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?

regards,
Pabzzmike

You need an SMS gateway. If you search this website you'll find some.

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

I highly recommend using an industry leader. This is so that you're not just using an SMTP "SMS" messenger.
Try Clickatell. They look like they have a high reputation online.