If there are problems with Registration please double check the logs to see the exact reason why 3CX is not registering normally to the Callcentric servers. Usually this is the same password for your email account. 0:0 UNKNOWN_TRANSPORT target domain=unspecified mFlowKey=0 ] replied: 408 Request Timeout internal. 3cx sip register failed 3CX Phone System takes on the corporate mobiles.