That summary says it all: it would probably much more convenient to have reply notifications via ICQ/IM (instead of eMail).
Does phpBB support this feature at all?
I'm quite certain that we won't be doing this with the current phpBB 2 codebase, and I can't find any existing extensions for phpBB 3 with a quick look (pretty sure it's not natively supported either still), so for the time being it doesn't seem like this is feasible. Thanks for the report though!