Methods are disclosed for identifying the carrier to which a phone, such as a mobile phone, subscribes in real time, at the time a call is originating from or terminating to the mobile phone. Where both parties to a call are subscribers to the same carrier, the methods can be used for applying preferential call rates to intra-carrier calls, e.g., making the calls free. The methods are particularly useful in the telephony networks with local number portability, in which the mere identification of the phone number does not necessarily identify the carrier to which the phone subscribes. The methods can use either existing databases to identify the carrier, such as LERG (Local Exchange Routing Guide) tables, number portability databases, name databases, and home location registers, or a new database can be created correlating mobile phone directory numbers with carriers.