Eircom says it expects to clear 800 faults today.
It follows extensive lightning in the west, south-west and east of the country, where 7,800 customers are without service.
The worst affected areas are currently Carlow, Kilkenny, Waterford, North Cork, West Cork, Kerry, Galway and Mayo.
The firm says 200 crews have been recalled from leave and will be working on St. Stephen's Day.