We can multi-task but we can't bend time. Thus there are still 24 hrs in a day. If Twitter is tipping, and i think it is, what will it cause us to spend LESS time doing? For me all of these one:many or many:many communication tools reduce the amount of time i spend on the phone. Basically for two reasons:
1) I can communicate more quickly with a wider range of people online
2) My "need for people" is (unsatisfyingly?) periodically satiated by email/IM/twitter and i feel less interested in speaking at length on the phone.