Forrester Consulting estimates a 401% ROI for a typical large organization that deploys a centralized SIP trunking topology using Acme Packet E-SBCs. The Total Economic Impact of Acme Packet’s Session Border Controller, which is based on separate and independent research by Forrester, indicates organizations save by eliminating underutilized TDM trunks serving each location as well as lower per-minute rates that apply to VoIP usage. In fact, each of the customers that Forrester interviewed reported a 40%-60% reduction in monthly service fees upon replacing T1/E1 TDM trunk lines with SIP trunks. Obviously, savings is directly proportional to the number of TDM trunks eliminated.

via Why do Enterprises Favor Centralized SIP Trunking Topologies?.