I have had a lot of questions about how I have achieved this functionality on a website. Well it's all pretty easy really, once you manage to find a provider to send the messages on your behalf!
Bluemini uses a company in South Africa called Clickatell who make our life very easy. You just sign up for an account, stick some credits and then decide on which API you want to use. I'm using the HTTP API which makes life very easy, just pass in your the text message, delivery number and your account details and they do the rest.