It's only a requirement, not a question.
You want an URL, so:
- either find a website which is providing this service
- or developp your own web service to handle this task
Guiding you through the entire process won't be possible; you have to put a minimum effort from your side.
A quick search lead me to this:
developping a sms send web service
And the first search result leads here:
Sending SMS using .NET through a Web service