Telefonica and Vodafone have announced a "wide-ranging strategic programme" to share mobile networks across certain European operations.
Largely a cost-sharing, and therefore saving, measure, the "milestone" announcement will see the two companies sharing their respective 2G and 3G networks now and going forward for future sites.
This will involve consolidation of existing sites and joint build of new sites, something the two operators are also angling as eco-friendly as fewer mast sites will be needed.
The cost saving is estimated to be in the region of hundreds of millions of pounds for both companies over the next 10 years.
Vodafone and Telefonica promise customer benefits to the team-up, including improvements to coverage, including mobile broadband coverage and thanks to reductions in network costs, the development of "innovative products and services for customers".
The countries affected by the agreement are Germany, Ireland, Spain and here in the UK where Telefonica is known as O2.