<script> <?php $this->callfunction($product) ?> </scipt>

<catalog_product_view>
    <reference name="content">
       <block type="<name>/catalog_product_callfunction" name="callfunction" output="toHtml"
              template="catalog/product/callfunction.phtml"
              as="callfunction"/>
  </reference>
</catalog_product_view>

class <Company>_<Name>_Block_Catalog_Product_Callfunction extends Mage_Catalog_Block_Product_View
{
   public function getCallfunction($product){
     // return json
   }
}

<?php $_product = Mage::registry('current_product') ?>
<script type="text/javascript">
     <?php echo $this->getCallfunction($_product); ?>
</script>

<?xml version="1.0"?>
<layout version="0.1.0">
    <catalog_product_view >
        <reference name="content">
         <block type="custommodule/custommodule" name="myscript"  template="catalog/product/myscript.phtml"/>
     </reference>
    </catalog_product_view>
</layout>

<?php
if(Mage::registry('current_product')){
<script type="text/javascript">
     <?php echo $this->getCallfunction((Mage::registry('current_product')); ?>
</script>
}
?>

<?xml version="1.0"?>
<config>
    <modules>
        <Amit_Custommodule>
            <codePool>community</codePool>
            <active>true</active>
        </Amit_Custommodule>
    </modules>
</config>

<?xml version="1.0" ?>
<config>
    <modules>
        <Amit_Custommodule>
            <version>1.0.0</version>
        </Amit_Custommodule>
    </modules>
    <global>
        <!-- start of block -->
        <blocks>
            <custommodule>
                <class>Amit_Custommodule_Block</class>
            </custommodule>
        </blocks>
    </global>

</config>

<?php
class Amit_Custommodule_Block_Custommodule extends Mage_Catalog_Block_Product_View{

    public function callfunction($product){
    $arr=array(
    'name'=> $product->getName(),
    'sku' =>$product->getSku(),
    );
    json_encode($arr);

    }
}

<script type="text/javascript">
    var optionsPrice = new Product.OptionsPrice(<?php echo $this->getJsonConfig() ?>);
</script>