Hardly any of them actually work still, like I said most service providers stopped people using thier email2sms gateways ( for free anyway ) to send messages when WAP was introduced to the public at large, and that is the only way you can get messages to a mobile without having access to an smsc, and unless you're really sad, and want to spend 6 months with an old nokia and a draw full of sim cards, searching for a smsc that allows free messages ( VERY RARELY ONE BECOMES AVAILABLE, EVEN THEN IT LASTS A MATTER OF HOURS ) then you're pretty much stuck.....
If your website makes a revenue then it might be an idea just to buy a service from somewhere.
Some US networks still allow you to send messages to thier phones for free, Cellular One, and Dobson, which I believe are owned by the same entity.
If you really wanna find out then phone up all the service providers you can think of in your country and ask them, normally if they allow it you would send emails to
number@isp.tld and they would relay the message to the phone.
The thing is with that is you'll have to know what codes belong to what networks else the messages will be emailed to the wrong gateway and never delievered, and as mobile companies each get new blocks of numbers regularly that's an almost impossible task.
