TSPI - TAPI Service Provider Interface

MSDN online: http://msdn.microsoft.com/library/en-us/tapi/tspi/telephony_service_providers_start_page.asp contains documentation and specification

MSPI - Media Service Provider Interface

MSDN online: http://msdn.microsoft.com/library/en-us/tapi/tapi3/media_service_providers_start_page.asp contains documentation and specification