Magento fax field replace with mobile number

Open file app/locale/en_US/Mage_Page.csv 
Paste the below code at last line
"Fax","Mobile"

For changes in admin panel Go to admin->system->configuration-> customer configuration 
And open the address template tab. Then replace all F (Fax) With M (Mobile) in all tabs
1. Text
2. HTML
3. PDF
4. JavaScript Template
The changes will be work on all order,invoice,shipment history and email all places.

Magento Set reviews limit on product page

Copy /app/code/core/Mage/Review/Block/Product/View/View.php to
 /app/code/local/Mage/Review/Block/Product/View.php. with following code :-

Find the function getReviewsCollection() and replce with below function.

public function getReviewsCollection()
    {
        if (null === $this->_reviewsCollection) {
            $this->_reviewsCollection = Mage::getModel('review/review')->getCollection()
                ->addStoreFilter(Mage::app()->getStore()->getId())
                ->addStatusFilter(Mage_Review_Model_Review::STATUS_APPROVED)
                ->addEntityFilter('product', $this->getProduct()->getId())
                ->setDateOrder();
                $this->_reviewsCollection->getSelect()->limit(5);
        }
        return $this->_reviewsCollection;
    }

Add Payment Method Custom column in admin > sales > order

1.)  Copy /app/code/core/Mage/Adminhtml/Block/Sales/Order/Grid.php to
 /app/code/local/Mage/Adminhtml/Block/Sales/Order/Grid.php. 

And replace with this function.

protected function _prepareCollection()
    {
         $collection = Mage::getResourceModel($this->_getCollectionClass());
         $collection->join(array('payment'=>'sales/order_payment'),'main_table.entity_id=parent_id','method');
         $this->setCollection($collection);
         return Mage_Adminhtml_Block_Widget_Grid::_prepareCollection();
         // end here //
    }

2.)  Search the function _prepareColumns() and add below code in this function
 

$payments = Mage::getSingleton('payment/config')->getActiveMethods();

        $methods = array();
        foreach ($payments as $paymentCode=>$paymentModel)
        {
                $paymentTitle = Mage::getStoreConfig('payment/'.$paymentCode.'/title');
                $methods[$paymentCode] = $paymentTitle;
        }

        $this->addColumn('method', array(
                'header' => Mage::helper('sales')->__('Payment Method'),
                        'index' => 'method',
                        'filter_index' => 'payment.method',
                        'type'  => 'options',
                        'width' => '70px',
                        'options' => $methods,
                ));
        // End here