High Quality Content by WIKIPEDIA articles! Series 40 is a software platform and application user interface (UI) software on Nokia`s broad range of mid-tier feature phones, as well as on the Vertu line of luxury phones. It is the world`s most widely used mobile phone platform and found in hundreds of millions of devices.. Analyst estimates place the total number of devices shipped with S40 close to 1.5 billion, as of the end of 2010.