What is different on UO is that you spend the "quality time" with other players: things like go fishing, decorating home or walking around woods, especially on RP servers you act and talk as a character, which makes a lot of difference to IMs somewhere else and talking about IRL stuff.

In GuildWars 2 iI spend "quality time" defending castles and killing enemies we use not IM but VoIP, which adds much more to the experience.