Eircom says it can't say when a major problem - which has affected hundreds of thousands of people - will be fixed.
Mobile and landline services - as well as ISDN lines - have been down since just after 10 o'clock this morning.
Eircom says they haven't yet identified the cause of the problem - which is intermittent - and technicians are working to resolve the issue.
Dublin Fire Brigade has tweeted to say its been advised by Eircom that using landlines to contact emergency services may be difficult.
Childline has also tweeted that children trying to use its service may be experiencing problems.
Customers can't call the customer care centres - so are being advised to report the fault online.
Director of Corporate Affairs at Eircom Paul Bradley says the fault is being investigated:
Our 999/112 system is fully operational for calls. Subscribers may face intermittent problems from affected landlines & mobiles #eircom.
— Dublin Fire Brigade (@DubFireBrigade) September 2, 2015
We are still experiencing some issues with our phone lines due to an Eircom fault . Alternative numbers available http://t.co/ni1wGdPhsw
— ESB Networks (@ESBNetworks) September 2, 2015
Important!! Children trying to contact #Childline number might experience problems due to Eircom issue. Go to Childline.ie for help. Pls RT
— ISPCC Childline (@ISPCCChildline) September 2, 2015
