Well, it seems that the Windows Phone 8 update, codenamed "Portico", will include the expected stability fixes, like addressing random reboot issues and the softness of Lumia 920 still pictures. SMS call rejection is also to be rolled into Portico.
It's not yet clear whether the update will be universal, i.e. introduce stability fixes across WP8 devices as well, or is it strictly addressing Nokia Lumia issues. The HTC 8X already got one update, but it seems that Microsoft was just testing the OTA system, so we are still waiting to see what will follow.