Clearly ever since the introduction of digital switching, telephone exchanges and PBX's have depended on computers for their operation, but CTI does not refer to that. CTI denotes the integration of application software that runs on PC's, minicomputers (in call centers) and mainframes (in big call centers) with the international telephone network.

The main categories of CTI software include:

Interactive Voice Response (IVR) - The familiar automated attendant that says "Press 1 for Sales, 2 for Customer Service etc." In its more sophisticated incarnations it can provide database lookups with synthesized speech for things like bank account balance inquiries or stock quotes.

Voice Mail - This is often combined with IVR systems, but can stand alone.

Database integration - When the phone company delivers the calling number as the phone rings, all sorts of applications can benefit. Traditionally the calling number is used to pull up the customer record for the caller before the agent starts to talk to them. It can also be used for verification that the caller is who they say they are.

This useful feature is now available to the masses, with the advent of Caller ID.

Call Control - Traditionally this has been provided in large call centers, for applications such as ACD (Automatic Call Distribution) or predictive dialing (the computer makes the call, and connects to a waiting agent if the customer answers. This is why you should just hang up when you answer the phone, say "Hello" and hear a few moments of silence).

With the advent of Windows Telephony, Call Control can now be done on the desktop, and used not for ACD or predictive dialing, but simply for making and receiving calls as you would with a regular phone. Except much easier and more powerful. The computer can walk you through conferencing and transferring calls with a series of prompts. You can dial numbers simply by highlighting them, and when the phone rings, the computer can display your records of the calling party.