The €22.8m (£14m) investment comes after "careful evaluation" of the Symbian OS and strengthens Siemens' commitment to the operating system for mobile phones, Siemens said in a statement. Siemens took out a license for the Symbian OS last year.
Symbian's software, available in phones today, competes with Microsoft's emerging Windows-powered Smartphone 2002 and Palm's OS for phones. All these operating systems add personal digital assistant functionality to a mobile phone.
Siemens bought the stake from Symbian's existing shareholders - Nokia, Matsushita, Motorola, Psion and Sony Ericsson.