Check http://www.nowsms.com or http://www.kannel.org
These are 2 SMS gateways the first one is commercial and runs under windows
the second is free and open source and runs under linux. You can communicate
with both using HTTP from your c# application. I use kannel (that runs on
linux) with my C# application (that runs on windows) and it is working fine
sending a large number of messages everyday.
The cheapest way is to contact a mobile phone company and subscribe to E.g.
a SMS webservice. Some of them are (nearly) free if you accept a small
advertisement in the end of the message.
If your SMS provider support service such as Mail2SMS you can use
System.Mail to send SMS message with C#, else you'll have to use third party
products to suport such functionality
Tamir Khason
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