The high-level design gives you a fairly accurate picture of your end-goal and the process you must take to get there, allowing you to later fill in the details on the exact steps and configurations that will be needed for everything to fit together. By this step, you should finalize the subscriber migration approach. (Flash-cut or phased? If phased, how many phases?) You should also have a basic understanding of what the final topology should look like. (How many Cisco Unity servers will there be? How will subscribers be spread across them?)
