d to expand the use of cellular services, but to bet- ter contain costs there is a need to expand their internal communications network. One of the direct effects is the increased use of Single Number Reach (SNR) solutions in enterprise locations. With SNR solutions, when a call comes into the enterprise, the sig- nal is duplicated SO that both the person's desktop phone and cellular phone ring at the same time. This forking of calls requires that a single call into an enterprise can potential- ly use two trunks or channels for both signaling and media. When the enterprise primarily used TDM trunking, this was expensive and required a wholesale update of all the TDM trunking capabilities to double the number of trunks that a location would use as it adopted the SNR service across a wider number of endpoints. Chapter 2: Trends in IP Telephony 19 Adopting SIP trunking as a connection to the SP to replace the TDM connection has resulted in a change of some of these architectures. The changes can be seen as phases in the development of the services of integrating enterprise and cellular networks: Phase I: SNR service enabled via an outbound call on the TDM network. Currently, this is most-widely deployed and can require a major update of all the TDM connec- tion to handle the doubled load. Phase II: SNR service-enabled via an outbound call to the TDM network via a SIP trunk service. This is made available by a few SPs and offers the unique advantage of the physical medium not being the limiting factor. Calls are not channelized over a TDM connection, SO the number of calls can grow to fill the IP pipe, and the IP pipe can grow at a much larger pace than the TDM pipes. Phase III: SNR service-enabled via an outbound call to the TDM network via a SIP trunk service, but the signaling is the only component that goes to the enterprise. The media is optimized and stays at the SP. This optimization enables the IP-PBX to stay in control of when the call is sent to the SP cellular network and maintains billing for these types 