Lexur - 6:17 am on Mar 30, 2013 (gmt 0)
...the one-on-one telephone call.
It's not the call what catchs the people, it's mainly the group chat.
It's the new "IRC at hand" and into closed groups of no more than 20 people with a clean interface and no ads, parents or bad people promoting p**n sites.
And, of course is cheap; almost free.