The first step is to get a script that is able to represent the email into an SMS text message. TheAnarchist suggested some good scripts.
However the next step is to find an email to SMS gateway. This costs money for every SMS text message sent out via the gateway. The pricing will depend on where you live and the facilities enabled by your Communication company.
There are a few sites which offer this service. You create an email account there and forward the mails from your site to this account and they will notify you about the new mails. Check rediff.com and if you are in Delhi/Bombay, India you may wish to try mtnlmail.com service. These services cost you some money
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