SMS Validation Plugin
SMS Validation Plugin allow you to protect your WordPress website by adding SMS verification functionality to User Registration and/or Comments functions of your website. Apart from standard registration, user needs to enter valid mobile number during the registration. In just a couple of seconds, user receive SMS code to mobile device. In order to login, user needs to validate that code against SMS Validation form in login section.
Plugin is using CS Networks HTTP API to send messages, meaning you will need a valid CS Networks username and password in order to be able to send SMS messages. Account can be obtained for free at http://www.cs-networks.net with approximately 20-40 free messages to test the functionalities. After that, credits may be purchased from CS Networks website.
For the complete list of covered mobile operators worldwide, please refer to: http://www.cs-networks.net/index.php/messaging/coverage