Some more traces for the PeerUnavailableException:

Testing the Sip stack !
Entering setupSipstack
Entering setupStackProperties
Success getting the Host IP address : [ 192.168.2.4 ]
Success setting the Stack IP address : [ 192.168.2.4 ]
Finished setting Stack properties
javax.sip.PeerUnavailableException: The Peer SIP Stack:
gov.nist.javax.sip.SipStackImpl could not be instantiated. Ensure the
Path Name has been set.
        at javax.sip.SipFactory.createStack(SipFactory.java:312)
        at javax.sip.SipFactory.createSipStack(SipFactory.java:153)
        at appletphone.ua.sip.SipManager.setupSipStack(SipManager.java:118)
        at appletphone.ua.sip.SipManager.init(SipManager.java:88)
        at TestSipStack.initStack(TestSipStack.java:13)
        at TestSipStack.main(TestSipStack.java:22)
Caused by: java.lang.reflect.InvocationTargetException
        at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
        at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:39)
        at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:27)
        at java.lang.reflect.Constructor.newInstance(Constructor.java:274)
        at javax.sip.SipFactory.createStack(SipFactory.java:304)
        ... 5 more
Caused by: java.lang.NoClassDefFoundError:
EDU/oswego/cs/dl/util/concurrent/ConcurrentHashMap
        at gov.nist.javax.sip.stack.SIPTransactionStack.<init>(SIPTransactionStack.java:314)
        at gov.nist.javax.sip.SipStackImpl.<init>(SipStackImpl.java:202)
        at gov.nist.javax.sip.SipStackImpl.<init>(SipStackImpl.java:243)
        ... 10 more
The Peer SIP Stack: gov.nist.javax.sip.SipStackImpl could not be
instantiated. Ensure the Path Name has been set.