I worked in a place that had 3 digit extensions. All extensions were DID's and the numbering plan ran like this:
Main bldg. xxx-n500 - xxx-n699
warehouse xxx-n700 - n799
satellite office xxx-n800 - n899
This whole plan was put in when converting from multiple 1A2's to a full Fujitsu PBX setup (1 Starlog, 2 Focuses). The leading digit of the three digit extension was a routing digit for the remote switches.
Users complained when they were transferred from one site to another that they could not take their numbers with them, but neither myself nor my vendor knew any other way to route them.
Because of this and NANPA issues the Fujitsu stuff was dumped in favor of Mitel SX-2000's at each site, plus 2 more sites, (ahh, the booming 1990's!)and another block of 200 DID's
We kept the 3 digit numbers but with DPNSS we were able to put numbers anywhere.
At my next company, we also had 3 digit extensions locally, but to call anywhere else in the company(worldwide), we dialed 8+xxx-xxxx to use the corporate net.
Bottom line, I guess, is how many users you eventually expect to have - 1000 with 3 digits or 10,000 with four. As far as enduser complaints go, most of 'em would bitch if you hung them with a new rope...
jsaxe
