Mobile network Three suffered an embarrassing services meltdown - just hours after an investment announcement hailing the firm as a major market competitor.
Around 400,000 mobile phone and broadband customers were left without service following a complete network outage for almost four hours on Monday.
The systems failure - for which Virgin Business Media has taken responsibility - occurred at around 9am as news emerged that the company agreed a deal to buy its rival O2.
A spokesman for Three Ireland said it was "unfortunate" that the network outage coincided with the announcement of the 850 million euro buy-out, but insisted both occurrences were "entirely unrelated".
"We offer our sincerest apologies to all our customers and for any inconvenience this may have caused," the spokesman said. "But the terms of the broader announcement today remain the same. There will be continued investment in the Three network and that will only see services improving for our customers."
The outage occurred just after 9am and services were down until around 1pm.
Third party provider Virgin Business Media confirmed a software upgrade it carried out had resulted in the Three outage.
"As part of a programme of work which Virgin Media Business began last month, a software upgrade today caused a temporary outage on the Three network in Ireland," Virgin said in a statement. "Service was restored by lunchtime. Virgin Media Business apologises to the customers of Three Ireland for any inconvenience caused."
Earlier, Three owner Hutchison Whampoa said the deal struck to buy O2 will give the firm the scale and strength to "compete even more aggressively" in Ireland. The deal with O2's Spanish owner Telefonica will see Three's market share increase to 37.5% and two million users - compared with the biggest competitor Vodafone and its 40% share.
"The outage was unfortunate from a Three point of view given the timing of events, but we apologise for any inconvenience caused," the Three spokesman added.