Voice over IP (VoIP) is undoubtedly one of the most rapidly emerging technologies in today’s telecommunication industry. With its widespread acceptance, VoIP is all set to redefine the way world communicates. However, there is a huge potential threat from spammers who could take advantage of its wide spread acceptance and cost effectiveness of VoIP. Even though SPam over Internet Telephony (SPIT) is still considered as an emerging problem, it is gaining increased attention from several research communities, universities and industries. Various algorithms and techniques have been proposed to combat SPIT. In this paper we focus on the Progressive Multi Gray level (PMG) approach proposed by Shin et al [1]. We have analyzed the behavior of the PMG algorithm for various call patterns and proposed a way of fine tuning the performance of the PMG algorithm for better blockage of SPIT.