Remote Site Settings:

Sample Code:

Without Media URL:

/**
   * Handles outbound SMS messaging via the Twilio REST API.
   * Sends a text message from a configured Twilio number to the specified recipient.
   */
  public class TwilioSMSHandler {

      /**
       * Sends an SMS message to the given phone number using Twilio.
       *
       * @param strPhone  Recipient phone number in E.164 format (e.g. +1XXXXXXXXXX)
       * @param smsBody   Text content of the SMS message
       */
      public static void send(String strPhone, String smsBody) {

          // Best Practice: Move credentials to Named Credentials or Custom Metadata Types.
          // Hardcoded values are a security risk and make rotation difficult.
          final String fromNumber = 'FROM_NUMBER';
          String strAccount       = 'ACCOUNT_SID';
          String token            = 'ACCESS_TOKEN';

          // Build the HTTP POST request targeting the Twilio Messages endpoint
          HttpRequest req = new HttpRequest();
          req.setEndpoint('https://api.twilio.com/2010-04-01/Accounts/' + strAccount + '/Messages');
          req.setMethod('POST');
          req.setHeader('Content-Type', 'application/x-www-form-urlencoded');

          // Encode credentials as Base64 for HTTP Basic authentication
          Blob headerValue = Blob.valueOf(strAccount + ':' + token);
          String authorizationHeader = 'Basic ' + EncodingUtil.base64Encode(headerValue);
          req.setHeader('Authorization', authorizationHeader);

          if (strPhone != null) {

              // URL-encode all values to safely handle special characters
              req.setBody(
                  'To='    + EncodingUtil.urlEncode(strPhone,    'UTF-8') +
                  '&From=' + EncodingUtil.urlEncode(fromNumber,  'UTF-8') +
                  '&Body=' + EncodingUtil.urlEncode(smsBody,     'UTF-8')
              );

              try {
                  Http http = new Http();
                  HTTPResponse res = http.send(req);
                  System.debug('Response Body is ' + res.getBody());

                  // Twilio returns HTTP 201 Created on success
                  if (res.getStatusCode() == 201) {
                      System.debug('Twilio Success ' + strPhone);
                  } else {
                      System.debug('Twilio failed ' + strPhone);
                      ErrorResponseWrapper erw = (ErrorResponseWrapper) JSON.deserialize(res.getBody(), ErrorResponseWrapper.class);
                      System.debug('Twilio error ' + erw.message);
                  }

              } catch (Exception e) {
                  System.debug('Exception is ' + e);
              }
          }
      }

      /**
       * Maps the Twilio API error response body for failed requests.
       */
      public class ErrorResponseWrapper {
          public String code;
          public String message;
          public String moreInfo;
          public String status;
      }
  }

With Media URL:

public class TwilioSMSHandler {  
      
    public static void send( String strPhone ) {  
      
        ErrorResponseWrapper erw;  
        String smsBody = 'Test Message';  
        String strMediaURL = 'IMAGE_URL_WITH_EXTENSION';  
      
        final String fromNumber = 'FROM_NUMBER';   
        String account = 'ACCOUNT_SID';    
        String token = 'ACCESS_TOKEN';  
      
        HttpRequest req = new HttpRequest();  
        req.setEndpoint( 'https://api.twilio.com/2010-04-01/Accounts/' + account + '/Messages' );  
        req.setMethod( 'POST' );   
        req.setHeader( 'Content-Type', 'application/x-www-form-urlencoded' );  
        Blob headerValue = Blob.valueOf( account + ':' + token );  
        String authorizationHeader = 'BASIC ' +  
        EncodingUtil.base64Encode( headerValue );  
        req.setHeader( 'Authorization', authorizationHeader );  
          
        if ( strPhone != null ) {  
  
            req.setBody( 'To=' + EncodingUtil.urlEncode( strPhone, 'UTF-8' ) + '&From=' + fromNumber + '&Body=' + smsBody + '&MediaUrl=' + strMediaURL );  
            try {  
              
                Http http = new Http();  
                HTTPResponse res = http.send(req);  
                System.debug( 'Response Body is ' + res.getBody() );  
                if ( res.getStatusCode() == 201 )  
                  system.debug( 'Twilio Success ' + strPhone );  
                else {  
                      
                    system.debug( 'Twilio failed ' + strPhone );  
                    erw = ( ErrorResponseWrapper )json.deserialize( res.getBody(), ErrorResponseWrapper.class );  
                    system.debug( 'Twilio error ' + erw.message );  
                      
                }  
            } catch( Exception e ) {   
              
                system.debug( 'Exception is ' + e );  
                  
            }   
              
        }  
              
    }  
      
    public class ErrorResponseWrapper {  
      
        String code;  
        String message;  
        String moreInfo;  
        String status;      
          
    }  
      
}