@Blaise and Josh:
Thanks for your help.
Its working now! I have made few changes by removing callback and straight 
away writing a code like below:

 geometry_msgs::PoseWithCovarianceStampedConstPtr msg = 
ros::topic::waitForMessage<geometry_msgs::PoseWithCovarianceStamped>("amcl_p
ose");

   ROS_INFO("Received X:[%f] :: Y:[%f] :: Z:[%f] ", 
msg->pose.pose.position.x, msg->pose.pose.position.y, 
msg->pose.pose.position.z);

- Prasad