The Java Platform, Micro Edition (the same thing used to have a "2" in there, and is still mostly referred to by that abbreviation) is a common platform for running applications on practically all featurephones, worldwide. It was developed by Sun, so is now owned by Oracle. Installation methods vary, and some applications will work on basically all devices, while some are targeted to specific operators, regions, manufacturers or classes of devices. J2ME runs on over three billion handsets right this minute (1Q 2012). This is still a big deal.
It is not just used on Featurephones, but also on bada, Symbian OS, Windows CE, Windows Mobile, Maemo, and MeeGo (alongside native software. There is even a download to run J2ME apps on Android.
Java ME Landing Page a bunch of introductions, as well as developer resources, from Oracle.