Pre-internet days, I found a safely guarded phonebook in the house. It also backed up as an address book. It was usually near the phone. I did not know its value. I had a good idea what my TV would be worth if I had to sell it. Now we have data points on what the address book is worth for leasing/sharing with the outside world.
Facebook bought Whatsapp few years ago. Radio talk show hosts were amazed at the price. I was not. The access to the phone book was implicit to this app — you shared your phonebook in return for the free app. And that trade was worth $42 per phonebook.
With LinkedIn purchase by Microsoft, we had a second data point. Keeping the math very simple, the professional address book was worth $60 per LinkedIn user. [26.2 Billion and 433 million users] This does not factor in value of social network data, adjustment for cash. Even more value for the address book if we divide by active users.