People will always find alternative routs to get the end that they want. As long as two people would like to do it the Skype way, they'll find a way to make it happen.  Before things got techy, one person could just easily go to his neighbor and negotiate an exchange of sorts. If they get to an agreement, they have a transaction. For most portable stuff, things other than Skype may already be in use as a vehicle for the processing of the transaction.