Cell phones or address books?

A few months joined the 21st century and finally bought a new cell phone. I figured that 4 years was enough for my tired phone. It's amazing what cell phones have become and how vital they for finding a phone number. Since my phone was too old, I had to write all the phone numbers down and I realized "Why are some of these people in here?" Granted some were work contacts, but there were people in there that I've never called and my phone served as an address book. I came across my written phone list this weekend and realized I didn't include a few numbers, hence my thinking on this topic. My realization is that I haven't needed the numbers in 3 months and I have them written down if I ever need them.