sending SMS messages to mobile phones

I'm interested in developing an application that will send an SMS message to
a mobile phone, but I'm not sure where to start. The purpose of the
application would be to send an SMS message to a list of cell phone numbers,
regardless of what phone provider they use. Is this idea viable? People have
suggested that they use email to send the message (i.e. (E-Mail Removed))
but some companies don't offer that service, so that wouldn't work. I'd like
to send it directly to the phone.
For this I'll be using C#.
Thanks.