Eir now estimates that about 150,000 customers are without broadband, telephone and mobile services as a result of Storm Ophelia.
The company said the storm had delivered unprecedented and widespread levels of damage to its infrastructure, including damage to poles and cables.
It said that while damage has been sustained throughout the country, the southwest and midlands are the worst affected areas and in particular Co Cork, where 51,000 customers have no phone service.
The company said it expects the numbers of customers without service will continue to fluctuate today.
"Some services will return as power supply issues are resolved. However, we do expect the number of individual fault reports to rise today and over the coming days," the company said in a statement.
Earlier, Eir had warned the number of people without a phone service may rise significantly throughout the day as back-up batteries that had been supporting services in some exchanges and mobile sites ran out of power.
The company said it had deployed up to 70 mobile generators to provide fixed and mobile services in locations that will restore services to the greatest number of customers.
Eir said about 1,200 staff will continue to work today to assess network damage and commence repair work.
But given the overhead nature of its network in rural areas, the damage is extensive and repair work will take time, it added.