Sony Ericsson is to acquire UIQ, the Swedish Symbian-subsidiary that produces the user interface for the handset manufacturer's high-end smartphones.
The deal announced on Tuesday has been agreed in principle, and is expected to be completed within the next few months.
"UIQ offers excellent technical flexibility enabling us to provide compelling features such as push email, internet browsing, end-user personalisation and enhanced music applications" said Mats Lindoff, Sony Ericsson's chief technology officer.
"By acquiring UIQ Technology we will further invest and exploit the full potential of UIQ on Symbian OS for phone vendors, mobile operators, developers and consumers."
Symbian's chief executive officer, Nigel Clifford, said the move would "strengthen the capabilities and services available for phones based on UIQ and Symbian OS while allowing us to focus on the core product development of Symbian OS for the mass market".
Sony Ericsson is already by far the most significant licensee of the operating system (OS), with UIQ version 3.0 being used on the recent P990, M600 and W950 handsets.
The move is the latest chapter in an complex relationship between the three organisations. Mobile Applications Lab, the company that went on to become UIQ Technology, was originally set-up by Ericsson Mobile Communications in 1998. UIQ Technology eventually became part of Symbian Ltd in 1999 with the new company known as Symbian AB.
"Most of the investors in Symbian must have been fairly down on subsidising Sony Ericsson's software development," suggested analyst Dean Bubley, of Disruptive Analysis, on Tuesday. "Motorola is not using it any more — essentially, the Sony Ericsson smartphone platform was being paid for by Symbian."
Bubley linked the announcement to Monday's news that influential operator Vodafone was pushing for a reduction in the number of handset operating systems, with the hope of concentrating on Windows Mobile, Symbian/Series 60 and Linux within the next five years.
"Given Sony Ericsson's resurgence in the last year or so, there is an argument that if it is serious about this, it will take UIQ and make it into their equivalent of Series 60," said Bubley, adding that this strategy would make it easier for Sony Ericsson to negotiate a place for its own preferred OS at the operators' high table.