Hi,
There are so many premium sms service providers available. you can also send from way2sms or other provider. but they have some limitation. Choosing best SMS provider is like choosing best service of hosting.
I am using service from
http://buzznx.com/[
^] as this was my first company as my professional life. You can search in google and ask them for demo. And most of the companies are providing Dot Net API along with SMS package.
Hope this information helps you,
Thanks
-Amit Gajjar