More than 300 new call centre jobs are to be created in Derry to service a mobile phone network provider.
The investment by US firm Convergys will see the company support EE customers.
EE was first to bring 4G coverage to the UK in 2012 and is the only provider in Northern Ireland.
Olaf Swantee, chief executive of EE, said: "I'm very proud that EE is leading the UK telecoms industry, delivering not only the first but the biggest and fastest 4G network for the country and within 18 months I want to be able to say that EE has done for customer service in the UK what it has done for networks.
"A major step of this is returning customer service jobs to the UK, where performance has been shown to exceed that of overseas contact centres."
4G, or fourth generation mobile telecommunications technology, provides improved access for internet users as more stream videos or make calls over the internet.
A total of 333 new jobs are being created by Convergys. Invest NI offered £1.5 million towards the development.
Convergys chief commercial officer Mike Wooden said: "By combining our extensive experience supporting many of the world's top telecommunications companies with the highly skilled and talented workforce in this region we can create a delivery centre that will generate meaningful benefits for Convergys clients, and more importantly, extensive career opportunities for the local workforce."
Stormont Enterprise Minister Arlene Foster said the investment would generate £5 million for the local economy every year.
Representatives from Convergys and EE participated in a discussion with Prime Minister David Cameron at last October's investment conference in Northern Ireland.
Ms Foster added: "It is welcome news today that we have been able to turn those discussions into tangible results.
"Invest NI's offer of support was also crucial to convincing Convergys and its client to choose Northern Ireland as the base for its new customer service centre."
Foyle SDLP MP Mark Durkan said EE are market leaders.
"EE's decision is a vote of confidence in Derry as an investment location and also recognition of the calibre of the local workforce."