IP trunking is the logical first step in implementing IP telephony. It is implemented using an ICP that includes an integrated VoIP gateway and PBX that connects to a WAN data trunk for both voice and data traffic. IP trunking results in measurable cost savings—some organizations have reduced their long distance charges by as much as 75 percent. But, as we will see later, this is more than just saving transport costs.

Municipalities can use their existing data infrastructure for voice services, starting with basic voice over IP trunking today and later adopting more sophisticated services such as unified messaging and remote teleworker support. IP trunking allows municipalities to create virtual tie lines that carry voice traffic over the data network between offices. These virtual tie lines improve bandwidth efficiency and reduce the cost of voice communications transported off the local premises—to other offices or to headquarters—by bypassing the toll network. IP trunking also enables the use of intelligent call routing and a uniform dialing plan (for example, five-digit dialing to any office, regardless of location).