Although CTI APIs have existed in various forms for more than two decades, early applications were often specific to closed, proprietary applications or platforms, and they lacked a compatibility that would allow horizontal integration with other communications applications.
Despite sitting next to one another on tens of millions of desktops, the telephone and computer have remained very poorly integrated. Analog modems are widely used, but do not support voice or many network capabilities, though that has changed with the development of UniModem V and related technologies. Still, analog modems are typically incompatible with the digital PBX telephone systems found in most offices. Other types of telephone networks abound, many of which are equally incompatible with today's modems, including Integrated Services Digital Network (ISDN), cellular, Centrex (a popular "virtual" PBX service offered by phone companies), and key systems (small PBXs), amongst others.
Microsoft provides a unifying platform for these two most common business technologies—the telephone and the personal computer. The Windows Telephony API helps bridge the gap between the telephone and computer by helping the PC to "understand" how telephone networks operate, and by letting programmers exploit network capabilities from within regular Windows-based applications.
Microsoft has been working with developers and vendors throughout the computer and telecommunications industries to create open APIs upon which all can build. The TAPI specification, introduced in 1993, was developed in conjunction with over 40 companies, including major chip and computer manufacturers, telecommunications equipment vendors, software developers, and network operators from around the world. Since then, the number of organizations contributing to the definition of TAPI's evolution has grown significantly making TAPI truly an industry-defined API. TAPI 2.0 represents a significant advancement of the API.