EIRCOM customers were brought on a time-trip yesterday, courtesy of the millennium bug.
Subscribers who inquired about their telephone bills through an automated dial-in service had their account balances backdated to 1900, decades before phones were commonplace in the State.
The millennium bug struck the company for several hours yesterday despite earlier "pretty confident" predictions. This follows an investment of more than £25 million to keep it at bay.
The glitch affected users of an interactive voice facility which allows customers to check their account balance by using the touch tones on their telephone.
People who called 1901 for the automated account inquiry service were told by a prerecorded voice that their outstanding balance related to January 1st, 1900, instead of January 1st, 2000.
The Y2K fault is likely to have bemused Eircom customers as the telephone was only invented in 1876. The first Dublin exchange in 1880 had only five customers.
Eircom's Y2K project director, Mr Dave Murray, last night described the glitch as "a minor irritant" in an otherwise smooth transition to the new millennium.
"It's at the trivial end of things to go wrong. Unfortunately, it's also highly visible, but c'est la vie," he said.
"We prefer that it was something like this rather than bills going out incorrectly or people being unable to make calls. We got the important things right but missed one of the little trimmings."
He stressed that telephone bills would not be affected.
The company was unaware of the glitch until it was contacted by The Irish Times yesterday afternoon. The problem was rectified by 8 p.m.
The millennium bug is caused by a computer programming oversight where years are identified by their last two digits. For example, 1999 is represented as 99. So when the year 2000 appears, the computer automatically assumes it is referring to 1900.
According to Mr Murray, yesterday's minor fault lay in a piece of software which transfers data from Eircom's billing system to its automated account inquiry service.
Callers who used the service yesterday will be disappointed to learn that they have no prospect of paying their phone bills at 1900 currency levels.