Some carriers feature billing options that allow the users to pay for the subscriptions in just a few easy steps. One of those is the MSISDN, that is, the Mobile Station International Subscriber Directory Number. It is used for identifying a mobile phone number, regardless of the country where it is based. The MSISDN is made of a country code, as well as a code that identifies the users cellphone carrier. This technology is basically is the mapping of the phone number to the SIM card. The main purpose of it is allowing the billing to be done directly, by charging the user through their cellphone balance.