Hi Bhaskar:
Your event handler looks fine to me. I am not sure what your UnRegister method does, but just to be clear the LINESTATE_UNREGISTER* events are not going to occur until after sipxLineRegister(lineHandle, false) is called.Are you getting the LINESTATE_REGISTERED state?
Did you invoke sipxEventListenerAdd before the line was registered or at least before the line was unregistered?
Also just to be sure we are talking about the same code base, what svn repository are you workinng off of?
You may also find sipxEventToString to be useful in debugging your event handler.
Cheers,
DanSent from my Android Xoom