Vat-Validation is a PHP class allowing you to

• Validate a VAT number
• Retrieve information like the name or the address of the company

The data is extracted from a European Commission webservice

It actually only works for European countries

require_once('vatValidation.class.php');
$vatValidation = new vatValidation( array('debug' => false));
$vatValidation->check($countryCode, $vatNumber));

Your instance can now access the following methods:

$vatValidation->isValid()
$vatValidation->getName()
$vatValidation->getDenomination()
$vatValidation->getAddress() 

You'll find an example in the example.php file

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Take a look at http://ec.europa.eu/taxation_customs/vies/viesdisc.do to know when/how you're allowed to use this service and his information