Symbian os is d best.......
Create powerful apps for the world’s most popular smart phone platform with Symbian C++
Symbian provides a secure, reliable operating system for smart phones and is created in Symbian C++
Symbian C++ has been designed to run efficiently on devices with relatively limited memory and power resources. Several elements of Symbian C++ therefore differ from desktop C/C++ because of these requirements. Specific examples include a leaving mechanism that protects apps against a lack of requested resources and special handling of data through descriptors. While these mechanisms may be unfamiliar at first, once mastered they enable the coding of robust and efficient apps.
For othr info check this: http://www.forum.nokia.com/Develop/Other_T...es/Symbian_C++/