Fujitsu must enjoy coming up with these theoretical technologies, because they certainly put out a lot of them.
Anyway, I believe Nextel in the USA offers something similar to this (a walkie-talkie style option), except that it is o­nly for two people at a time. That, and I believe it's just a glorified cellular protocol, and the functions of the service are integrated into the phone as opposed to Nextel itself. But I could be way off base.
Fujitsu's system uses IP networking (whether it be cellular or wireless LAN), allowing for multiple users to take advantage of the technology at the same time. Since it's packet based...well, you would have to face data charges instead of minute charges. But that's what unlimited packet transfer is for :)
Hopefully this article will explain the technology better than I just did.

Fujitsu Labs and Fujitsu have developed "Ubiquitous Transceiver Technology," a packet technology that uses cellular networks or wireless LAN to allow multiple people to vocally communicate at the same time.

"Ubiquitous Transceiver Technology" is a technology that uses IP networking, both cellular network and/or wireless LAN, to provide transceiver-like audio communication. The technology is also being dubbed PoC/W (Push-to-talk over Cellular/Wireless), and allows for multiple users in different regions to talk using packet transfer.

Recognizing the lagging advancement of packet-based audio communication, Fujitsu has developed a new audio data processing technology that will automatically optimize sound quality. For Ubiquitous Transceiver Technology, various features such as member state management, speaking power management (meaning, whether or not you have permission to speak o­n the network), and the usage of SIP/SIMPLE protocol for PoC/W notifications are employed. Audio data is compressed before sending, increasing response efficiency.

Fujitsu will first apply this technology to devices aimed at the corporate world, and then plans to expand it for an office solution or consumer use. The company is investigating support from cellular phone makers, and plans o­n commercialization within 2004. Furthermore, the same technology will be o­n display at the "Fujitsu Solutions Forum 2004" to begin o­n July 7th at Tokyo's International Forum exhibition.

Inspired by:
http://k-tai.impress.co.jp/cda/article/news_toppage/19479.html

Press Release:
http://pr.fujitsu.com/jp/news/2004/06/29-2.html