I assume that recent nokia's phones are great mainly because they cannot run any other mobile OS than Symbian EKA2 (main reason being that EKA2 is hard-realtime

I assume that recent nokia's phones are great mainly because they cannot run any other mobile OS than Symbian EKA2 (main reason being that EKA2 is hard-realtime microkernel with GSM/UMTS stack in userspace, while any other OS expects anything related to radio interface or telco protocols running on second separate CPU). And I assume that this is major reason, why Nokia can pump out reasonable smartphones with size and battery life of dumb feature phone with price certainly bellow other smartphones. (Well I have E90, which certainly is not small or was not cheap, but battery life is unsurpassed by anything, except 10 year old high-end Nokia phones).