The invention relates to a method and system for authorizing a commercial transaction between a customer and a goods or service provider via an authorization service provider with authentication of the customer by comparing a biometric sample of the customer with a biometric model of the customer stored with the authorization service provider. The telephone link between the supplier and the authorization service provider is set up via a router which associates the real telephone number of the authorization service provider and the telephone number of the supplier with a virtual telephone number and transmits a code which is isochronously calculated by the router and the authorization provider with the aid of the same algorithm. The telephone link is accepted by the authorization service provider if the supplier is registered with the authorization service provider if the supplier is registered with authorization service provider under the transmitted number and if the transmitted code corresponds to the calculated code contained by said authorization service provider. An identifier and biometric code of the customer are transmitted to the authorization service provider in addition to the amount which is to be transferred. The transaction is initiated by the authorization provider if the correspondence between the biometric sample and the stored biometric model exceeds a predetermined thresh old value.