A first invite message including a parent device identifier assigned to a parent device is received. The first invite message refers to an incoming call or an outgoing call. The incoming call or the outgoing call are then routed between a parent telephony application server (TAS) allocated to the parent device and a child TAS allocated to a child device. In some cases, the child device is a mobile child device that is registered with an Internet Protocol (IP) multimedia subsystem (IMS) network using a unique identifier that is associated with a child device identifier assigned to the mobile child device. The parent TAS is able to store the child device identifier and the child TAS is able to store the parent device identifier.