This is a Windows system installed file with Windows File Protection (WFP) enabled.
There are 44 versions of tapisrv.dll in the wild, the latest version being 6.3.9600.16384 (winblue_rtm.130821-1623). The average file size is about 254.01 KB. The executable is a .NET framework assembly utilizing the CLR.
The Telephony service implements Telephony Application Programming Interface (TAPI) services to support programs that effectively work the same way over intranets, the Internet, and traditional public phone networks.
(Note, the behaviors below are for all versions of tapisrv.dll, select a unique version for details.)
United States installs about 33.77% of Microsoft® Windows(TM) Telephony Server.