If you have multiple clients, it’s very easy to lose track of their phone numbers (if you even had them to begin with). That’s why every time that a client calls me and I don’t have their phone number on file, I add it to my cell phone (if they called on that) or my Microsoft Outlook Contacts section. Even if you have almost no interaction with this client, you never know when you might need to get a hold of them in a hurry. It takes only a few minutes, and yet it may save you from coming up short in a crunch situation.