In this paper, we design a stealthy GSM phone identity catcher. As the GSM protocols do not mandate the authentication of BSes (Base Stations) to MSes (Mobile Stations), fake BSes can be implemented to lure victims to register with and thereby intercept crucial information of the user, including their identities. However, the straightforward implementation of GSM phone identity catcher can be easily perceived by users employing detection software due to such phenomena as phone interface changes and service interruptions. In this paper, we propose several effective mechanisms, such as smart configuration of the fake BSes, quick attachment/detachment and service relay, to make the catching process invisible to users and software. Real world experiments have been conducted and the results prove the efficiency and stealth of our proposed GSM phone identity catcher. We hope our work could help to enhance the effectiveness of IMSI catching attack and thereby alert the industry to design stronger authentication protocol in communication systems.