Centrex is a collection of services offered in most parts of the US. Companies can simply run trunk lines from the Telephone Company Central Office (CO) into their company, and do not have to purchase a PBX. The PBX is actually at the CO, and is programmed and configured there. Centrex environments support hookflash transfers and individual extensions per user, as well as a range of other optional features. PhoneSoft fully supports Centrex environments. Centrex is usually used in smaller companies where they are not ready to purchase and manage a PBX. However, there are some large companies which continue to use Centrex. Centrex offers some enhanced features in some parts of the country, including an option to run a dedicated 64KB line to the customer site with calling and called party information. The customer can purchase or rent a modem box (~$5000) which connects to this dedicated line and provides standard SMDI information. PhoneSoft also supports this SMDI connection. .