Note: USA-specific Not even 20 years ago, before any number could be ported to mobiles, landlines in some (all?) Baby Bell regions had their prefix determined

Note: USA-specific Not even 20 years ago, before any number could be ported to mobiles, landlines in some (all?) Baby Bell regions had their prefix determined by geography. In other words, you could know what "zone" a given phone number was in by its prefix. Take Silicon Valley. A (650) 960-xxxx number meant Mountain View. (408) 733-xxxx meant Sunnyvale. Etc. Zones roughly respected cities, but boundary conditions abounded. If you lived near the Mountain View / Sunnyvale border, you could be in area code 415 (later 650) or 408. San Jose had 3 zones. Cupertino was part of SJ1. Fremont / Newark were lumped and spanned 2 zones. Milpitas was part of SJ2. etc. You were only guaranteed a local (non-toll) calling area of something like 8 miles, but Pac Bell would give you all of the zone overlap: if any part of your zone was within that 8 (?) miles of any part of your destination zone, it was a local (free) call. This meant your actual local range could extend 20+ miles. I set up PC-based call broadcast systems (the vendor product I used was "BigmOth" for some membership organizations such that I could send a recorded message to whatever numbers in a given member roster. By placing two parallel systems in, say, Sunnyvale and SJ3, I could cover everywhere from Menlo Park to Los Gatos to Coyote to Fremont Newark zone 1 with no variable phone costs. So, I set up a table in my database to join prefixes to zones, and my program went through the contacts and routed each destination number to the appropriate calling phone book (I rewrote the phone books after every batch of database updates). I had one system in my house, and a colleague had one in his in SJ3. I'd just uploaded his share of the phonebooks and the message recording binary to his ftp site, leaving him maybe 10 minutes of work for each cycle's setup. Thus, I could blast 2-minute messages to members over a 200+ square mile area for free. It was really slick. 10 years later, it was irrelevant, as everywhere became a free call.