A mobile device includes multiple subscriber identification module (SIM) cards. When a user of the mobile device requests to call a phone number, the mobile device determines a mobile telecommunications service provider of the phone number, based on service provider information received for the phone number from a service mapping server. The mobile device selects for the call a SIM card from the multiple SIM cards that is associated with the determined service provider of the phone number. The mobile device places the call to the phone number using the selected SIM card.