WordPress Text Message v. 2.06
GPL 3+ license
WordPress Text Message is an SMS plugin that allows users to signup for SMS text message updates to your WP website or blog. All you have to do is add the signup form via widget or provided shortcode on a post or page.
By default the plugin has United States based cell carriers available, but new in version 2.06 is a plugin settings page "Carriers" - that allows you to edit, remove, or add cell providers email to SMS text gateways. What this means is that (for the first time) the plugin is usable to international website owners (outside the U.S.) for the first time. With the ability to edit your own carriers, the plugin now works for any geolocation.
Screenshot, details, and PDF list with 325+ SMS gateways worldwide are on the official release page: