Knowing What Part Of Town Someone Lives In By Their Phone Exchange
| Field | Telecommunications |
| Went Obsolete | 1996 |
| Made Obsolete By | Local number portability (LNP-the ability to assign a phone number to a line on a different exchange or carrier) |
| Knowledge Assumed | The ability to notice patterns in exchanges and remember them |
| When useful | Phone numbers that have not been ported to a line on a different exchange or to another carrier |
The exchange (or prefix) of a telephone number used to be specific to an exchange, or central office (which connects you to other exchanges, and the rest of the global telephone network). That was why if you moved, even within a city, you might have been assigned a new phone number.
This started to change in 1996 when the FCC began to require LNP.
If you have had your phone number at the same place since before 1996, your exchange will, of course, still reflect the part of town in which you live.
Going back even further, up until the early 1970s, it was common for people to give the telephone exchange number in place of the first two digits of their seven-digit phone number. The exchange name often was based on the street where the exchange was located. For example, a person whose phone number was 737-4031 would typically give out their phone number by saying “Pershing 7-4031” (on the phone dial, the letter 'P' was on the '7' and the 'E' was on the '3'.) Some people would shorten this to PE7?-4031. This all went away long before 10-digit dialing, but that's a whole other topic of discussion.
