Easy Send SMS wordpress plugin is simple plugin to send SMS using any of the commercial SMS gateway.
below are the list of sms gateway that ESS supported.
SMS Global
http://smsglobal.com/
Twilio
http://twilio.com/
Nexmo
http://nexmo.com/
OnewaySMS
http://onewaysms.ph/
You can find, download and install Easy Send SMS directly from the
Plugins section in WordPress.
or go to this link
http://codemywebapps.com/wp-plugins/easy-send-sms/
If you want to install manually, download and unzip the easy-send-sms.zip file and upload to the
/wp-content/plugins directory. Then activate the plugin through the
Plugins section in WordPress.