This little module is for verifying a vat number (UID) through a SOAP webservice (http://ec.europa.eu/taxation_customs/vies/checkVatService.wsdl).
After installing this module you get a additional option in details-tab to check the field, if it is a real UID.
https://modules.processwire.com/modules/inputfield-uid/
https://github.com/hintraeger/PW-InputfieldUID