Abstract: In this study, a covert communication applying the vector quantization based information hiding algorithm and the Public Switching Telephone Network (PSTN) is implemented. The system aims at offering good security of the secret binary image message and the real-time performance that is very important for the speech calling of the telephone service. Therefore, we adopt a simple and effective encryption method for the secret binary image message prior to the embedding process. The embedding position is also protected by using a secret key. By using these methods, the requirement of short-term protection in the bursting phone call communication for the secret binary image message and the real-time encryption are both fulfilled. Furthermore, an information hiding algorithm based on vector quantization is proposed and the advantage of it is discussed. We evaluate the system with the ITU-T G.729a standard speech codec in StegoPhone, which is our platform for research on covert communication technology via PSTN. The experimental results show that our method has negligible hearing effects on the conversation speech and meet the requirement of the real-time calling conversation communication via PSTN.