We offer open source PHP, Java and Perl APIs for automated access to the Telephone Verification service. The APIs are bundled with the minFraud APIs.
This mod will enable you to specify the dollar amount minimum at which a customer will be contacted by MaxMind's automated telephone validation system. The customer will be instructed in the checkout_payment page that they must enter a phone number at which they will be contacted. The customer will be given a random, 4-digit code by the automated phone call. They will have to enter this random 4-digit code in the Order Confirmation page in order to complete the order.
Brian Repetti has posted an ASP script to call Telephone Verification.