Before mobile phones, people kept contact diaries to record their contacts.
Modern mobile phones allow you to save a lot of numbers easily. Numerous contact numbers can be stored easily on mobile phones.
A simple search in your phone's address book is all it takes to find someone's phone number.
Google Drive can be used to backup your contact number. The contact number of someone should never be lost.
Whenever and wherever you need a contact number, you can find it with no hassle