According to this study from December 2014, these are OS brands used for mobile phones hones:
Android, iOS, Java ME, Symbian, Windows Phone, BlackBerry, Kindle, Samsung, Bada, LG, Windows Mobile, ZTE. The last 6 have under 0.1% market share each.
I think any OS requires some form of maintenance - feature and security updates at least.
In my opinion BlackBerry (10) is the most stable because it's kernel (QNX Neutrino) has only 100.000 lines of code. QNX was and is used in nuclear plants, defense networks and medical applications - and will be used in Ford cars too. For other details read this article.
