Application of the Internet protocol (IP) as a network technology for telephony has the power to revolutionize the telecommunications industry. The bandwidth is flexible and almost free, and new services can easily be introduced. This abundance of services and bandwidth is the promise of IP telephony. Before this promise can be fulfilled, however, IP telephony needs to mature and bridge the gap to current telephone systems: the public switched telephone network (PSTN), the integrated services digital network (ISDN), and the wireless systems. Transferring telephone service to the IP domain is not a simple task. Solutions used in switched telephone networks may not be appropriate for the data world. On the other hand, the data world creates its own problems - addressing, reliability, and security are some examples. Initially, these problems may seem best solved by reusing protocols and ideas from the switched telephone world and adapting them to IP. However, tomorrow's problems may be created by such solutions. For example, should an IP telephony service be encumbered with legacy issues such as in-band tone signaling? In this paper, we give an overview of interesting issues in this area and provide a framework in which solutions to small problems can contribute to reaching the final goal of an IP-based telephony service.