Just thought that i'd add to this thread my experience of the new Nokia E72 which i bought yesterday to replace my old E90. If anyone is interested/forced to explore GTD on a symbian device I'd say you cant find a better tool than this. Build quality is superb, it has everything a smartphone is required to have (if you prefer a physical qwerty over touchscreen and want a non-slider) and the in built PIM is IMHO better than anything I've used so far. You are forced to use tags for categories (like @calls) in the description field of the task to substitute for the actual lack of categories in symbian, but in exchange you'll get the best search function for sorting task-lists/contexts that (atl least) i've ever played with (and I've used palm, winmo, uiq). The same applies to notes, documents etc if you want to have some context on these too. And the syncability (?) with other platforms (outlook, gmail) is flawless.
-Jukka