Dixons Carphone is to launch its own mobile phone network this spring, with the retailer using Three's existing infrastructure.
The deal comes after electrics retailer Dixons, owner of Currys PC World, merged with phone seller Carphone Warehouse in 2014, and will see the newly formed Dixon Carphone partner with Hutchison Whampoa, the Hong Kong owner of Three.
Launching this spring, the network builds on the retailer's existing mobile broadband relationship with Three and will offer "highly personalised connectivity options for customers to enjoy."
Known as a mobile virtual network operator (MVNO), the network will be branded as Dixon Carphone, but customers will be connected to Three's masts and network infrastructure, similar to how networks like Tesco Mobile and Giffgaff use O2's service.
Sky will also offer a mobile network over O2's infrastructure, having agreed a deal in January. The new network, to be sold alongside Sky's existing television, broadband and home phone services, will launch in 2016.
The news comes at a busy time for Three and the UK mobile industry as a whole, as Hutchison is currently in talks to acquire O2 for up to £10.5 billion. Meanwhile, BT is in the process of buying the EE network for £12.5bn.
The announcement of a new network "supports our strategic vision to continue to offer customers the widest range of connections, for when they are at home or on the go," Graham Stapleton, CEO of Carphone Warehouse, said in a statement.
Speaking to the Financial Times, Stapleton elaborated: "We will have something different from what is available elsewhere in the market with a more personalised service for the mobile customer that will let them tailor their price, minutes and data to their changing needs."
The network has been developed as a way of serving Dixons customers who buy connected products like smart television, as well as laptops and computers.
Lynda Burton, director of wholesale at Three, said: "This is our biggest new customer to date and a great opportunity to be the MVNO partner of a large scale brand with real mobile expertise and insight."