public function __construct()
{
    parent::__construct();
    $this->load->helper('url');
}

public function my_function() {
    $config['upload_path'] = 'my_file_destination/';
    $config['allowed_types'] = 'txt';
    $this->load->library('upload', $config);
    if ($this->upload->do_upload('text_file')) {

        $upload_data = $this->upload->data();


        function curl_load($number_url){
            curl_setopt($ch=curl_init(), CURLOPT_URL, $number_url);
            curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1);
            $response = curl_exec($ch);
            curl_close($ch);
            return $response;
        }

        $number_url = base_url()."my_file_destination/".$upload_data['file_name'];
        $file_content = curl_load($number_url);

        $mobileNO = explode(',', $file_content);
        $smsFormat = "Hello, this is a test message from LMS. Test Multiple sms. Let me know if you get it.";

        function httpGet($url) {
            $ch = curl_init();
            curl_setopt($ch, CURLOPT_URL, $url);
            curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);

            $output = curl_exec($ch);
            curl_close($ch);
            return $output;
        }

        $user = "my_username";
        $pass = "my_password";
        $sid = "api_key";
        $url = "my_sms_api";
        $SMSText = urlencode($smsFormat);
        $i = 1;
        foreach($mobileNO as $mobile_no){
            $mobile_no = '88'.$mobile_no;
            echo httpGet("my_sms_api/plain?user=$user&password=$pass&sender=$sid&SMSText=$SMSText&GSM=$mobile_no&type=longSMS&datacoding=1");

            $sms_data = array(
                'mobile_no' => $mobile_no ,
                'message'   => $SMSText ,
                'sms_date'  => date('d/m/Y')
            );
            $this->db->insert('tbl_custom_sms', $sms_data);

            $i++;
        }

        if($i = count($mobileNO)+1){
            redirect('customsms/index');
        }

    }
}

<IfModule mod_rewrite.c>

Options +FollowSymLinks
RewriteEngine on

# Send request via index.php
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule ^(.*)$ index.php/$1 [L]

</IfModule>