A voice over Internet protocol (VoIP) system. The system includes a first device and a second device. The first device is disposed in a wireless local area network (WLAN) and connected to an Internet, for performing voice communication with a remote device through the Internet. Additionally, the first device processes audio information received during the voice communication to generate at least a playback audio packet, sends out the playback audio packet through the WLAN, receives at least a captured audio packet through the WLAN, and processes the captured audio packet to generate audio information to be sent out during the voice communication. The second device is disposed in the WLAN, for receiving the playback audio packet through the WLAN, playing audio information contained in the playback audio packet, capturing outside audio information to generate the captured audio packet, and sending out the captured audio packet through the WLAN.