Exchange Note and Task support in MS Activesync was added in Exchange 2010. From that point on it is the handset manufacturers decision whether to include/exclude certain activesync capabilites.
I have an android currently and have to use the touchdown sofware to get notes functionality - but it does work perfectly. The issue is that none of the handset manufacturers (apple included) - have decided to add in the addtional task/notes functionality into their native activesync support.
Im aware of touchdown for android being a very good program on the android that supports the notes/tasks.
Im currrently looking for a similar program for apple - as quite a few of our staff have signaled their intention to move away from blackberry onto iphones.