Eircom said there are still some 11,000 unrepaired faults on its lines today following severe weather and storm damage in recent days and it warned that some customers may be without a service until late next week.
The company said today the true extent of the damage to its nationwide network had now become clear.
"Since the storm recovery plan has been activated, more than 6,000 faults have been cleared. Despite these efforts by 1,400 staff working on the ground, an additional 4,000 faults have been reported in the past 24 hours. The current number of total faults stands at more than 11,000," Eircom said in a statement.
"The storm damage nationwide is severe and continues to impact every county in Ireland with Dublin being the only exception. While there are no communities complete isolated, north Mayo is the worst affected with more than 600 faults. The western seaboard, Louth, south Kilkenny and Waterford remain badly affected."
Eircom said its call centres were handling "an exceptionally high level of calls".
"Additional customer service representatives have been put in place to help deal with the increased call levels."
The company said it had put its "full resources into restoring service as soon as possible" but that it could take until late next week to restore service to many customers.