Three, which recently closed a deal for up to €850 million to buy O2 Ireland, has struck a deal with Nokia as part of what it says is a €300 million investment in the company's enlarged network.

Three, which is also rolling out its 4G network nationwide, has hired the Finnish company, better known for its handsets, to upgrade its older 2G and 3G networks.

Nokia will supply new base stations for the older networks, as well as a cloud-based system for managing the system.

Three said work would begin on the project in September, and it would be completed by 2017.

“Customers will start to benefit from the improvements before then,” the company said.

Three's recent purchase of O2 makes it the clear number two operator in the market with 37 per cent share, just behind Vodafone.