A method for communication includes modulating a stream of data in accordance with a voice-band modem specification, so as to generate a modulated signal. The modulated signal is up-shifted to generate a passband signal, which is transmitted over a telephone line simultaneously with a baseband voice...http://www.google.com.hk/patents/US6934368?utm_source=gb-gplus-share專利 US6934368 - Multi-band modem
