I answered a similar question to this yesterday:
Sending Bulk Sms Using VB.NET[
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The second option seems quite cheap for sending messages internationally. I don't know of any service local to you though.
For examples on how to use Tropo, here is a good link:
http://blog.tropo.com/2010/11/08/using-c-to-send-outbound-calls-and-sms-messages/[
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You will need to convert the code to VB.NET from C#, but that isn't hard (you can even use an online conversion tool to get you most of the way there).