User terminal, and method and device for providing mobile communication service are provided. The method includes: a first subscriber card providing service through a first network, and a second subscriber card providing service through a second network; detecting that the first network currently supports providing a first type of service for a plurality of subscriber cards at the same time; notifying other subscriber card except the first subscriber card to allow the other subscriber card to provide the first type of service through the first network; detecting that the second subscriber card needs to provide the first type of service; and if performance of the second subscriber card providing the first type of service through the first network is better than performance of providing the first type of service through the second network, controlling the second subscriber card to provide the first type of service through the first network.