Irish mobile phone users pay on average five times more for their calls than users in the cheapest EU country.
That is according to new data from the European Commission, which says a real single market for telecoms is needed.
The EU data shows a huge disparity of nearly 800% between what mobile phone users in the cheapest and most expensive member states in the union pay.
The country with the least expensive mobile phone costs is Lithuania, where consumers pay 1.9 cent per minute.
In Ireland, the cost per minute is 10.2 cent.
The most expensive country is the Netherlands at 14.7 cent per minute, while the EU average is 9.1 cent.
The European Commission says the price differences cannot be explained by differences in quality, cost of providing the service, or consumer purchasing power.
European Commission Vice President Neelie Kroes said it is critical for the EU to move quickly to build a real single market for telecoms.
She will present a new package aimed at strengthening that market next month.
In a statement, Comreg said: "Aggregate costs per minute do not necessarily indicate the cheapest offer available in the Irish market and there is a significant variation in these costs across the operators.
"There is also no distinction between pre- and post-paid customers."
Comreg said that according to research carried out by Telligen, the cost of mobile post-paid packages in Ireland is below or close to EU average while the cost of pre-pay packages is above the average.
It added that costs in Ireland are converging to the EU average.
"In 2010, Average Revenue Per Minute was 13 cent in Ireland compared to EU average of 11 cent while in 2011 ARPM was 10.2 cent in Ireland compared to EU average of 9.1 cent.
"In 2012 Irish ARPM was 8.5 cent - EU ARPM in 2012 was 10.3 cent."