That's very cool. When I was a kid, a nearby department store (Fred Meyers on 39th and Hawthorne) used a large-scale DECT system for employee-to-employee and paging. Each staff member carried what was essentially a ruggedized cordless phone with an earpiece and they heavily used DECT's "intercom" handset-to-handset feature to talk to each other, and it was all on a PBX with their outside phone lines. I believe it was a Panasonic system. Panasonic seems to still offer such a setup that uses IP for coordination between the multiple DECT "cells," but I'm not sure what was in use at the time. I remember it giving me an overwhelming feeling that my home's DECT cordless phone was a disappointment to the technology's capabilities.

For that matter I once had a job where I had a WiFi IP phone that I carried around, but I think cellphones have gotten cheap enough for corporate users that the wind is out of those sails. I keep thinking about buying one of those on eBay...