I can't possibly see it being VIN specific. This isn't to fix an issue, it's to install a feature that was never on the car to begin with. Also, I don't know if it would qualify as a TSB since this isn't a recall issue. It's totally optional whether or not you get it done.
If you car doesn't have call waiting, then this should apply to you. Here's the letter.
370Z Call Waiting Letter
Call the number on the letter - Nissan Information Centre - 1-800-387-0122