8. For every month during which the provider must provide, at any time, a telephone service to a client, the provider must collect the tax at the same time that the provider receives from the client a sum for the telephone service.
Despite the foregoing, in the case of a client who, otherwise than by way of a subscription, subscribes to a telephone service by paying in advance a sum for the service, the provider must collect the tax at the time the service is provided for the first time in the month.