It has a closed user interface, so third parties cannot develop software for native application software, or install third party applications, unlike S60 and UIQ.
↑Chesbrough, Henry William; Vanhaverbeke, Wim; West, Joel, eds. (2014). New Frontiers in Open Innovation. Oxford University Press. p.83. ISBN978-0199682461. ... the next most important customer was NTT DoCoMo and MOAP (Mobile Oriented Applications Platform), whose handsets accounted for 10‒20% of Symbian sales...