from http://www.gsmarena.com/symbian_carla_and_donna_to_come_next_but_not_for_everyone-news-3394.php
«As far as the current Symbian Belle is concerned - Nokia X7-00, E6 and 500 are going to get the update until the end of this year, while the Symbian^3 (already updated to Anna) devices will receive it in Q1 2012. It seems Belle will be the last update for the Symbian^3 and Anna generation.»
there hasn't been any official release so far for Symbian^3 devices only "leaks", that is releases from NOKIA development without any backing of NOKIA; thus if your device stops working after you (tried to) install(-ed) one of those & you have to bring it to NOKIA Care Center, they may charge you to fix it.
or not...