Abstract: A wireless PBX system having at least one predetermined coverage area, and having a predefined group of mobile communication devices associated with each predetermined coverage area is provided. Each of the mobile communication devices belonging to a predefined group includes a first telephone number by which the mobile communication device may be reached via a wireless network, and a second, short extension number, identifying the mobile communication device as belonging to a particular group. Mobile communication devices within one of the at least one predefined groups may reach other mobile communication devices within their group or within another group by dialing the second extension number of the desired recipient mobile communication device, and may reach other communication devices not associated with any group by dialing an appropriate telephone number.