Some 200 homes in the Dun Laoghaire and Sandycove area of south Dublin were without telephone connections for the past week, after an underground cable was broken by a "third party".
A spokeswoman for Eircom described it as a "third party cable break" - where someone working on the road accidentally cut a cable.
Eircom received no report of the break at the time, she said. This was despite an obligation on contractors to contact Eircom before beginning work, so the company can provide maps showing where cables are laid.
All homes will be reconnected today, the spokeswoman said. She said "severe damage" was done to the cable.
Engineers have to replace 360 metres of underground cable and connect the cable with each home, she said.
The company will investigate the source of the break, she added.