Eircom technicians are continuing to work to restore full services following an "intermittent issue" on part of its network.
Mobile and landline services for some businesses - as well as ISDN lines - went down just after 10am this morning but standard fixed line numbers were not affected.
Progress has been made in restoring services in Dublin and in the southern half of the country - and engineers are continuing efforts to fully resolve the issue.
In a statement issued this evening, the company insisted that emergency numbers were not impacted.
"Eircom confirms that an incident on our core telephony network this morning has impacted approximately 5% of our daily call volumes," the statement read.
"The incident resulted in intermittent service that has impacted customers which use 1800 and 1500 numbers as well as some mobile numbers.
"Since the issue arose at 10am, we have made progress to restore service for impacted customers in Dublin and the southern half of the country.
"We have diverted traffic away from problematic points on our network and our engineers continue to work to fully resolve the issue as soon as possible.
"Calls to 999 and 112 have not been impacted.
Director of Corporate Affairs at eircom Paul Bradley said the company is sorry for the inconvenience caused to customers.
"We're trying to get to the route cause, but most importantly we're trying to restore services,
"So for those businesses that were impacted, in the south of the country and Dublin, those services have largely been restored, and we certainly do apologise for the inconvenience caused to anyone today.