The intelligent networks used in the cellular technologies today are vital for profitable growth for the network providers. Operators in today's competitive market are desperately looking to improve their profit margins and reduce operating expenses. Many of these networks are also reaching end of support and implementing Next Generation Intelligent Networks (NGIN) is the next step to overcome all these issues. However, replacing the legacy Intelligent Networks (IN) networks at once is not an economical option and operators want to integrate NGIN with the legacy IN. The paper highlights the functional entities of NGIN and suggests the solution to the problems caused while re-using existing IN in an IP Multimedia Subsystem (IMS) environment.