Buys out Ericsson's 50 per cent share for 1.05bn euros.
The deal has been rumoured for months and signals the renewed vigour with which Sony is approaching the connectivity business these days.
After years in the doldrums, the giant Japanese firm has received much praise for its tablets and connected TVs. With this takeover of its phone JV, the intention is surely to join up the various elements of its device family and thereby take on Apple, Samsung and even Amazon in the race the offer consumers a joined up hardware and software service.
The transaction also provides Sony with five essential patent families relating to wireless handset technology.
Sony's release is quite explicit about the reasons behind the move, stating: "The transaction gives Sony an opportunity to rapidly integrate smartphones into its broad array of network-connected consumer electronics devices."
Meanwhile Ericsson concedes that the JV makes little sense for a telco infrastructure firm any more.
"The synergies for Ericsson in having both a world leading technology and telecoms services portfolio and a handset operation are decreasing.
"Today Ericsson's focus is on the global wireless market as a whole; how wireless connectivity can benefit people, business and society beyond just phones."
However, it will now set up a 'wireless connectivity initiative' with Sony to drive connectivity across multiple platforms.
Sony Ericsson came into being in 2001, and enjoyed huge success in Europe especially with its Walkman and Cyber-shot feature phones.
It fared less well in the smartphone era, launching only one successful product family, the Android-based Xperia.