Another major function of a day planner is keeping track of phone numbers, hopefully in alphabetical order. This is slightly difficult on paper, unless you've planned ahead and left room for new numbers. Eventually you run out of room and spend time erasing or scratching out old numbers and writing in new ones. The HP 95LX's built-in Phone Book is very flexible, automatically alphabetizing PHONE lists, and allowing you to easily find and change someone's phone number.