Embodiments of this application disclose a communication method, a wearable device, a server, and a system. The method includes: obtaining, by a wearable device that is in a cellular-based Narrowband Internet of Things mode, an unreceived communication notification message from a server based on a preset period or a preset time point; and when a user needs to reply to the communication notification message, switching, by the wearable device, from the cellular-based Narrowband Internet of Things mode to a cellular mobile network mode to reply. According to the embodiments of this application, low-power voice paging of the wearable device can be implemented, and a usage time of the wearable device can be prolonged.