Customers reported issues across the midlands.
Three Ireland say difficulties with data services that affected customers today have been resolved.
However, the company says it is working to restore full service as soon as possible.
Customers reported issues in Athlone, Mullingar, Tullamore and Portlaoise.
In a notice on its website, Three says;
"The intermittent issue browsing the internet which affected customers today has been resolved. We are now working to restore full service as soon as possible. We would like to thank customers for their patience and apologise for any inconvenience caused.