There used to be talk of running out of phone numbers in the US between multiple-lines at home and work, fax machines, cell phones, etc. But not so much anymore. Why? Because of my daughter.
My daughter has a cell phone number. It could likely be the only phone number she ever has. She may never get a home phone. Fax machines, already becoming obsolete, will likely go the way of the typewriter by the time she grows up. I wouldn't be surprised if she never gets a separate office phone line either.
My daughter has an email address. It could also be her primary email for the rest of her life.
My daughter has a postal address. She has had many postal addresses and will have several more. Why not just have the USPS computers map some number (like her cell phone) to her current physical address which she can enter in a database. In a world where we are moving from identities pointing to people instead of locations, why should the old postal system be left behind?