It implements SmsSenderInterface that should be implemented by text message sender classes to be used in Yii2.
The preferred way to install this extension is through composer.
Either run
php composer.phar require --prefer-dist yetopen/yii2-sms-sender-interface "*"
or add
"yetopen/yii2-sms-sender-interface": "*"
to the require section of your composer.json file.