Guess we need an open protocol! OP should build that
As far as I've been able to find the only two mediums that match that friction are an email or a phone number. (And we're looking at adding text message support instead of just email)
A third medium is that most people have the ability to access a website. I built http://near.im/ (sorry for the ugly frontend) with this in mind. An advantage here is you don't have to communicate to another person your name or e-mail address (which can be hard for some people), just describe a short domain name.