Here's what its competitors are offering...
Three users were sent messages from the company yesterday informing them that a number of its mobile packages are changing.
It's €20 unlimited data package will be cut from 30 days to 28 days, adding up to 24 days less over the space of 12 months.
From April its prices are going up - users have a chance to cancel their contracts if they are not happy with these changes.
Commenting on the decision, Three told Newstalk, "This is the first time that Three has revised the cost of its core portfolio in a number of years. These changes are a direct result of the increase in costs of doing business. Notwithstanding the revisions, we still offer some of the most competitive plans on the market that are affordable and offer real value to our customers.
"We are the only mobile operator to offer All You Can Eat data and we have also taken this opportunity to add more value to our plans by allocating an additional generous data allowance, which, as well as the text and call plan allowances, can be used when roaming in the EU," the company added.
For data-hungry prepaid customers, Tesco Mobile offers unlimited calls, 10GB of data, and unlimited Tesco Mobile texts for €15 per month.
Meteor will give you 15GB data every month, plus unlimited calls - and "unlimited access to YouTube, Facebook, Snapchat, Instagram, Twitter, WhatsApp and Viber" for €20 every 30 days.
These are the new terms of Three bill pay deals:
These are the previous terms:
Three told Newstalk that it is "committed to maintaining our highly competitive position in the market, both on price and quality of service, and will remain industry leaders for data."