We don't need no stinkin phone numbers

Why do we need phone numbers? If you ask the average person, they will tell you that you need a phone number to call someone. I'm not sure that we need phone numbers.

A phone number is an interesting thing. What's more interesting is what it is not: it's not an attribute or property of a phone. That is, there is nothing in your phone (I'm thinking old-style land-line phone here) that knows its phone number. 

And that makes sense. I can take my land-line phone, unplug it from my house, carry it to your house, plug it in, and use it. When I do, calls made are charged to your phone number (your account) and not mine. The fact that I'm using the handset from my house doesn't matter.

One can view a phone number as an address, a target for phone calls. This is a pretty good description of a phone number. The phone jacks in your house are bound to a "pair number" at the central office, and a phone number is associated with that pair number. This level of indirection allows the phone company to move phone numbers around. For example, when my sister moved from one house to another in the same town, she kept her phone number. The phone company simply associated her phone number with the pair number associated with her new home.

Cell phones have a similar arrangement. There is no pair of copper wires running to a cell phone, obviously, but each phone has a unique identifier and the phone company associates your phone number with that identifier. Once associated, the phone company can route calls to your phone based on the identifier.

Another view of a phone number is that it is an instruction to a switching system. Specifically, an instruction to the public switched telephone network (PSTN) to connect you to a particular phone. This is a slightly more useful concept, since it binds the phone number to the switching system and not the device.

Binding the phone number to the switching system means that it is an artifact of the switching system. If we replace the switching system, we can replace the phone number. This is precisely what Skype does, and I suspect competing systems (Vonage, Google Phone) do the same thing.

With Skype, you don't need phone numbers. Instead, you use the Skype ID. I'm on Skype, and I can talk with other Skype users. To connect to another Skype user, I need only their Skype ID -- no phone number is necessary. The Skype switching system can connect us with just the ID.

Skype does let me call people who are not on Skype -- people on the PSTN. To call them, I *do* need a phone number. But this is not Skype's requirement; it is a requirement of the PSTN. (If you want to talk to anyone through the PSTN, you must provide a phone number.) When Skype takes my call and routes it to the PSTN, Skype must provide the destination phone number.

Just as phone numbers are instructions to the PSTN, and Skype IDs are instructions to the Skype switching system, URLs are instructions to the web system. (The switching system for the web is perhaps a bit more complex than that of the PSTN, as the web has multiple layers of addresses, but the concept is the same.)

We may soon see the decline of the phone number. It works for the PSTN, but not for other systems. Other systems (the web, Skype, Google Phone) have no need of phone numbers, other than to connect to the PSTN. If we abandon the PSTN for other systems, we will also abandon phone numbers.