Verify CELL Number By sending SMS

 Hi to all,
In my website (C# with asp.net 2.0) i collect cell phone numbers from customers.
My problem is : i just want to verify the cellphone number of my customer.
For that i want to send a small sms with verify code.
I just want to how to achieve this one with FREE with out Commercial SMS GATEWAYS.

I don't want to use Commercial SMS GATEWAYS.

Please give a valuable suggestion.

Thanks..
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