$company_name = new Zend_Form_Element_Text('company_name');

$phone_number = new Kwista_Zend_Form_Element_Phone_Number('phone_number');

<?php

class My_Form_Element_Phonenumber extends Zend_Form_Element 
{
    public $helper = 'formPhonenumber';

    public function setValue($value)
    {  
        if(is_array($value))
        {
            @list($first, $second, $third, $ext) = $value;	
             
            // saving comma-delimited for simplicity, save however you want
            // this is NOT the display
            $value = sprintf('%s,%s,%s,%s', $first, $second, $third, $ext);
        }

        return parent::setValue($value);
    }

}

<?

require_once 'Zend/View/Helper/FormElement.php';

class My_View_Helper_Phonenumber extends Zend_View_Helper_FormElement {
    
    public function formPhonenumber($name, $value = null, $attribs = null) {
        $info = $this->_getInfo($name, $value, $attribs);
        extract($info); // name, value, attribs, options, listsep, disable

        $value=$this->view->escape($value);

        // retrieve from comma-delimited list
        list($first, second, $third, $ext) = split(',', $value);
            
        $html = '(<input type="text" size=2'
                . ' name="' . $this->view->escape($name) . '[]"'
                . ' value="' . $first . '">)'
 
        $html = ' <input type="text" size=2'
                . ' name="' . $this->view->escape($name) . '[]"'
                . ' value="' . $second . '">'

        $html = ' - <input type="text" size=3'
                . ' name="' . $this->view->escape($name) . '[]"'
                . ' value="' . $third . '">'

        $html = ' ext. <input type="text" size=3'
                . ' name="' . $this->view->escape($name) . '[]"'
                . ' value="' . $ext . '">'               

        return $html;
    }
}