A radio talk show host chided himself for drawing a blank this morning. After mentioning that listeners could call in, he asked, "What's the phone number here? I've only worked here for 30 years."
Although my memory of phone numbers is generally strong, I understand why the host was flummoxed temporarily. When part of your work routine becomes so rote that you don't have to think about it, it's easy for it to slip your mind occasionally.
At work, I frequently have to refer callers to certain phone numbers that I've read off hundreds of times. Despite committing them to memory, I always read the phone numbers off of a form. While it's unlikely that I'll forget them, it's wise to always have that reference sheet handy--just in case.