There are no Reference Implementations (RI) or Compatibility Tests Suites (CTS) available for the Java Telephony API. The JTAPI specification is targeted at many different types and categories of telephony platforms including mobile phones, PBXes, IVR (interactive voice response systems), computer telephony servers, ACD (automatic call distributors), and call centers. These platform types have widely differing capabilities that require them to implement one or more optional sets of JTAPI packages and/or methods within a package in order to achieve the functionality desired by the industry. Many RIs and CTS, each customized to each telephony platform category, would need to be written to adequately cover all the target platform types. A comprehensive RI and CTS that covers and tests all combinations of optional JTAPI functionality would be exceedingly difficult to achieve in practice and be of questionable usefulness to implementers.
It sounds like you would have to get the jar from the vendor providing it and Sun is just providing the spec.
The reason it's not part of J2SE or J2EE is that it's a rather specialized API that few people need. In that sense it's similar to Java3D, JAI, JMF and others.
[ February 22, 2008: Message edited by: Ulf Dittmer ]