According to TRAI any pack that is activated by consumer by any channel (voice, USSD or SMS) is a two-step process. First the request is acknowledged then a confirmation is requested from the consumer. Only one when the consumer responds within a stipulated time, the request is taken up or it is discarded for good.
However, when it comes to Roaming Incoming free pack for Vodafone via USSD, the two step process is totally overlooked. You dial the USSD code and the requested is accepted for processing, the charges are debited from the main account and the pack is activated in a few minutes.