I can't answer out of personal experience, but I've seen guildmates connect on dial-up when their broadband was down. From what I've heard, its doable but it ain't pretty. You can chat and probably craft without too many issues, but I don't think combat (at least "intense" combat) is very playable, especially with the the new combat system. But again, I've never tried, so I could be wrong. Hope this helps.