Abstract: Methods and apparatus are described for maintaining established local calls at an access module in case of change of the call control for a distributed PBX over a communications network, e.g. WAN or LAN, especially an IP network. In accordance with a first main embodiment, the system is composed of one Call Server controlling the call processing of other PBX access modules in a normal situation. These access modules have the ability to operate in Stand Alone or Survival mode if the link to the Call Server is down for any reason. In a second main embodiment, two call servers may be used, an active call server and a hot-standby server. The active call server controls the call processing of the access modules. In case the link between one access module and the active call server fails, the hot-standby Call Server can take over the control of the access module.