Finnish mobile phone giant Nokia is paying 264m euros ($410m; £209m) to buy out the other shareholders in handset software firm Symbian.
Nokia, which already owns 48% of the UK-based firm, intends to develop its software to compete with Google's planned Android operating system.
Nokia said Sony Ericsson, Ericsson, Panasonic and Siemens had agreed to sell their stakes in Symbian.
It added that Samsung was also expected to accept the offer.
For its part, Symbian said the takeover was "a fundamental step" in the establishment of the Symbian Foundation, which is expected to start operating in the first half of 2009.
The foundation will bring together Nokia, AT&T, LG, Motorola, NTT Docomo, Samsung, Sony Ericsson, STMicroelectronics, Texas Instruments and Vodafone in collaboration on a new, royalty-free open software platform for mobile phones.
"The battle for your handset is under way"
According to Nigel Clifford, chief executive of Symbian, it could signal a sea-change in how the software platform is developed.
"We're freeing up innovation - this is epoch-making.
"Nothing like this has been put into the open-source community before."
The aim is to unite several different existing software programs - Symbian OS, S60, UIQ and MOAP.
The deal is a logical move, according to Handelsbanked analyst Karri Rinta.
"There was pressure for Nokia to increase its holding, especially since there were owners such as Panasonic and Siemens, who were there for historical reasons."
Android response?
The news comes one day after reports that Google's Android platform for mobile phones had suffered delays.
According to the Wall Street Journal, several firms who had signed up to the open-source platform were having difficulty coming up with their own custom applications in time for the planned launch later this year.
At a Symbian press conference, Kai Oistamo, executive vice-president of Nokia, denied that the takeover was a response to Android.
"This is taking the most proven software to open-source. It has an unparalleled existing ecosystem. It will create a gravitational pull that no developer will be able to ignore," he said.
But Geoff Blaber, an analyst with CCS Insight, questioned how open the platform will be.
"Can the new entity really be open when Nokia has such a vested interest? This may be the stated goal, but in practice it might be more difficult to achieve. We'll have to scrutinise the fine print of the intellectual property rights and articles of association," he said.
To date, more than 200 million Symbian OS based phones have been shipped and the operating system accounts for approximately 7% of the mobile devices market.
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