Lots of Java's enterprise applicability has to do with Enterprise JavaBeans, but the usefulness of the language extends far beyond multi-tiered client-server applications with persistent storage mechanisms at their back ends. The Java Telephony API (JTAPI) is becoming increasingly important as organizations work toward combining their voice and data communications onto a single network infrastructure. 

By putting voice and data on one network, even if it's just internally (i.e., inter-site traffic still goes over the public switched telephone network), significant savings in cost and complexity -- they're one and the same, really -- can be realized. JTAPI is nicely put together, and is robust enough that many big-name companies are using it. JTAPI is used particularly frequently with Voice-over-IP solutions.

JTAPI is concerned with call control, which is to say not the actual encoding and decoding of voice but rather the process of establishing a call, maintaining it as long as its parties remain engaged, and tearing it down when it's done. Call control also has to do with special connection tricks like conferencing multiple parties together and transferring a call from one party to another.

JTAPI also supports a set of events that are useful to developers of applications that need to be integrated with telephones. A Customer Relationship Management (CRM) application, for example, might need to know where a particular call was directed so as to pop the appropriate record on the answering party's workstation. A voicemail application could use JTAPI events to detect "ring out" on a telephone and grab the call for recording.

In Java, JTAPI is encoded in the javax.telephony.* packages. It provides for the instantiation of a Provider object (representing the switch that connects endpoints), an Address object (representing a termination point identifier -- a phone number, in other words), a Call object (representing a phone call itself), a Connection object (a connection is the termination of a call at some station -- a Call usually has two or more associated Connections). Once you have a call, you can use such methods as connect() and disconnect() to set up and tear down a voice link.