Millions of mobile users are left in limbo as Three is hit by power outage
Up to two million customers of Three Ireland were unable to make calls, send texts or use data yesterday as the company battled major problems with its network.
Some customers also reported problems with using the Three website for parts of the day.
The issue with service was fixed before 7am today.
The company thanked customers for their patience and apologised for any inconvenience caused.
A company spokeswoman said the outage was caused by an electrical failure.
"An electrical failure in one of our data centres caused the building's temperature to rise, which subsequently impacted some of our systems," she said.
Last night most of Three's services had resumed, but some customers still experienced problems.
Three recently added O2 customers to its ranks following the purchase of O2's Irish business last year. It is understood that former O2 customers - up to 1.5 million of them - were amongst the worst affected yesterday.
Three experienced a network outage on the same day last June that it announced the €850m deal.
Three is now the second biggest mobile provider in the country. It has a 32pc market share, with market leader Vodafone on 39pc.
Mobile phone usage in Ireland is one of the highest in Europe per head of population.