Vista - send SMS using C# 2.0

Hello everyone,

I just wanted to develop one web application which allows users to
send an SMS to any mobile free of charge or i can say that i want to
develop web application like www.160by2.com which allows users to send
SMS for free of charge and you can send the same message to multiple
people (Max 10) with full ajax support. I searched on the net and
found many codes and articles and through those articles i came to
know that for that kind of application, i required either of the
following things:

1. Web service (Third party web services that are free but not
working or not delivering the sms)
2. GSM Modem ( I don't have any idea about this)
3. SMS Gateway ( I don't have any idea about this)

I can use either of the following and my work will be done. but if i
can have free web service which is really working then it would be
great or even i am ready to pay for that but charge should be minimal
and support multiple message sending or suggest good gsm modem and how
i can make such an application with it.

Please guide me through this. From where do i start? and one more
thing is that does asp.net 2.0 have inbuilt libraries that provide any
facility to send an SMS.

Any help will be appreciated !

Regards,
Nil
"Never Expect..Never Regret"