Web SMS (Web to phone) Service

I need help to add a free SMS service to my country portal

[OnlineSupport]

I'm looking at adding a free SMS service to a country portal I run, as a means to attract more traffic to the site. The site is mainly advertising/AdSense driven, and traffic is essential to me.

I've seen a couple of great free SMS services out there, but I have no idea how to implement a similar service in my site.

-->Is it only a scripting issue, or do I need to purchase any equipment?
-->Do I need to make any payments to the receiving networks?
-->If any licencing is involved, how do free services (like AgentSMS) manage to reach worldwide networks?

In particular, I find the AgentSMS free SMS service to be really great (fast, anonymous, and trully international), but I've no idea how I can implement this within my portal, even to my limited reach.

If its only a scripting issue, are there any free / low-cost scripts out there? Any ideas would be most appreciated.