GO-Bulk-SMS

This application allows you to send thousands of SMS to a wide range of
customers. You don't need to pay anything for SMS Gateway, but FREE of
cost. This application used google voice API and sends SMS at free of
cost. You just need a Google Voice account and upload the mobile numbers you
want to send the SMS. You may save the mobile numbers in a text and
upload it. Later send SMS by bulk or single. Kindly note that Google
Voice is working only on limited countries like US/Canada. Please check
the availability and then use it.