How to Setup Bulk SMS Functionality on Contact

Login to your Salesforce Org where the package is Installed.
For Bulk SMS functionality, you have to create :-

Visualforce Page
Controller
Application

Change the name of object accordingly . (Example for Lead object, you have to write standardController = “Lead“ instead of standardController = “Contact“)

<apex:page standardController="Contact" recordSetVar="cons" extensions="SendBulkSMSActionController">
    
    
    <apex:includeLightning /> 
    <div id="LightningComponentid" />
    <div id="sampleContainer">
        <style type="text/css">
            .redAlert {
            font-weight: bold;
            color: #FF0000;
            font-size : 22px;
            text-decoration: none;
            text-align : center;
            }
            
        </style>
        
         <apex:form >
             <apex:outputPanel id="tstpopup">
                 <apex:outputPanel rendered="{!showLoading}" >          
                     <center>
                         <apex:outputText styleClass="redAlert" value="LOADING..."/><br/>
                     </center>
                 </apex:outputPanel>
             </apex:outputPanel>
            
            <apex:actionFunction name="getLoading" action="{!getLoadingValue}" reRender="tstpopup"></apex:actionFunction>
        </apex:form>
        
        <script>
        var GetIDs= '{!contactIds}';
        
        $Lightning.use("cm_datatransfer:SendBulkSMSApplication", function() {
            $Lightning.createComponent("cm_datatransfer:sendbulkSMSScreen",
                                       {
                                           //pass parameter values to lwc js controller
                                           listObjectIds : GetIDs
                                       },
                                       "LightningComponentid",
                                       function(cmp) {
                                           console.log('Insidedd');
                                           getLoading();
	                                       console.log('LWC Componenet added in VF page');
                                       });
            
            });
        
        </script>
        
       
    </div>
</apex:page>

/**
* Copyright (C) Cloud Maven, Inc - All Rights Reserved
* Unauthorized copying of this file, via any medium, distribution and packaging is strictly prohibited
* Proprietary and confidential
* Written by Cloud Maven <support@cloudmaveninc.com>, December 2019
*/
global with sharing class SendBulkSMSActionController {
    public List<Contact> getIDs;
    public String contactIds{get;set;}    
    public Boolean showLoading {get;set;}
    
    
    public SendBulkSMSActionController(ApexPages.StandardSetController controller){
        System.debug('Get Selected');
        showLoading = true;
       
        getIDs = controller.getSelected();
        contactIds = '';  
        for(Contact oContact : getIDs){
            contactIds += oContact.Id + ','; 
            System.debug('Contact ID : '+contactIds);
        }
        contactIds = contactIds.removeEnd(','); 
        
        //headerdata= ApexPages.currentPage().getHeaders().get('Host');
        //urlvalue=Apexpages.currentPage().getUrl();
        //url='https://' + headerdata+ urlvalue;
    }
    
    public void getLoadingValue()
    { 
        System.debug('Inside');
       
        showLoading = false;
        
    }
}

<aura:application access="GLOBAL" extends="ltng:outApp" >
    <aura:dependency resource="sendbulkSMSScreen"/>
</aura:application>

Now, we have to make button “Send Bulk SMS“.
Go to Source Object and then Go to Button,Links, and Actions

Click on “New Button or Link“.

Enter the details as shown in below snapshot.

Select the Visualforce page you have created.

Click Save.
Now, Go to Search Layouts for Salesforce Classic.

Click on Edit of List View Edit.

Select Send Bulk SMS button from Available Buttons and add it to Selected Buttons

Click Save.

You can see Send Bulk SMS button.