I don't think I will ever retire my N900 (until it's not functional, and then it will be replaced by another one).

Regarding repurposing it, I think a N900 is probably the best candidate to be repurposed out of any existing phone in the present, past (and perhaps in the foreseable future). To me the N900 is just a handheld computer with phone capabilities, so even if you stop using it as a phone, you are left with an awesome miniaturized linux computer.

So, in a sense, it wouldn't be repurposed, but merely used in all its capacities (minus the phone function, which in the context of everything is probably anecdotal considering what else it can do).

Use it as a gaming machine, programming platform, translator, learning tool (great document readers like evince, FBReader, etc), video player (with great video out capability), torrent downloader, incredibly capable MP3 player (almost limitless storage space, one of the best sound quality out of any phone ever, support for almost any codec imaginable)...

I suppose you get the idea.