As the name suggest, Free SMS is a web application that allows you to send free SMS messages to mobiles on selected networks.
At the moment, the networks are restricted to USA, UK, France, Sweden and Argentina. Within these countries, not all network operators are available but most major ones are. Using Free SMS is very simple - just enter the phone number you want to send a message to and select the carrier where you want your free SMS message will be sent. In the Reply To field you can type an email where you want to receive your answer.
It's not clear whether you have to add an international prefix code but we tried both ways without success. 10 minutes after sending a message it still hadn't arrived, so Free SMS isn't very reliable. Unfortunately, there's no help guide or developer support so it's a case of trial and error. It looks like the service is funded by Google ads that are placed on the screen when you open the Free SMS site and enter your SMS message.
Free SMS is a good idea although its functionality is dubious and there is no kind of user help section which would have been useful.