^ that's a more comprehensive link than what I posted. That's a much larger database
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i live in sri lanka..how to start free
you need to modify the alerts plugin or create a new one that simple sends and email and it will create a new profile option for SMS email addresses. Have your users provide an email address that sends to their SMS number. Simple as that, no need for a true SMS gateway/service.
this method is free, unless you want to pay someone to make the plugin for you.