A communication apparatus is provided. A first subscriber identity card camps on a first cell belonging to a first wireless network capable of providing a conference communication service for the first subscriber identity card with at most N peer communication entities via a first radio transceiver module. A second subscriber identity card camps on a second cell belonging to a second wireless network via a second radio transceiver module. A processor builds a conference communication for the first subscriber identity card with at most (N−1) peer communication entities via the first cell, receives an add request to add a new peer communication entity to the conference communication, adds the second subscriber identity card to the conference communication via the first cell, and adds the new peer communication entity to the conference communication via the second cell.