SMS Settings enable you to configure the unsubscribe methods and service provider integration for your SMS campaigns.
To reach SMS Settings, navigate to the SMS campaign listing page and click the Settings button. 
Under the General tab, you can select the appropriate Unsubscribe method and configure the Silent Hours and Campaign Prioritization settings.
The available unsubscribe method is to unsubscribe using a link or a keyword. You can also design your Unsubscribe Page to which your recipients will be directed when they click the Unsubscribe Link.
Silent Hours setting ensures that your text messages are sent during preferred times, avoiding the inconvenience of contacting your subscribers late at night or during other unsuitable hours. When you check the Enable Silent Hours option, you can set the time period to prevent the delivery of your messages to your users.
Campaign Prioritization setting lets you launch or schedule multiple campaigns in order and send messages faster. To enable it, check the Enable Campaign Prioritization option.
Campaigns are given priority based on their starting time. When you select the Send Later option in the Launch step of your SMS campaign, the campaign will be listed with a Scheduled status on the Prioritization tab.
Refer to Unsubscription Methods for SMS, Silent Hours and Campaign Prioritization for further details.