This exam will cause trouble for anyone that doesn’t have a solid understanding of all topics listed for this exam. While you can read and have a good understanding of the way things are approached when issues arise, without some type of hands on troubleshooting in a Unified Communication environment you will probably have some problems. This exam, in my opinion, is the hardest test in the CCNP VOICE track. Not only must you know how a technology or feature well, you have to also be able to resolve issues. The last area that might cause trouble are the steps hardware or features use to function / startup. You probably should now the steps IP Phones go through during boot up.
Call Routing is a major function of Cisco Unified Communication, it would be a very good idea to know where and how to use the tools available to isolate and resolve issues. The many parts that deal will call routing should be known very well to assist in problem resolution.
When dealing with phones, the problems can be wide and varied. You must know the path a call takes; you must also know how the phone is configured when it is at its home station or traveling to another site.