How can I send SMS messages like Twitter does?

Question

Do all cell companies have open APIs that allow you to send SMS messages like Twitter does?

Do you have to pay to do this?

Answer 1

Many (most?) mobile companies have email gateways allowing you to send an SMS. For AT&T I believe it's [email protected], but each provider will have a different address.

Answer 2

This wikipedia article summaries it pretty well. Some cell companies have easy formats. For example, Verizon uses [email protected].