Any, several couple months later they sold to AOL for something like $250 million. I was living in Chicago at the time and coincidentally the Hancock building had just sold for ~$280 million. I remember thinking that four guys had created as much value in a year as thousands of construction workers and real estate managers had created in three decades.
Their story is very interesting :) , the founders were Arik Vardi, Yair Goldfinger, Sefi Vigiser and Amnon Amir.
We talked to Yair, from what he told us, they were using dial-up at the time, and they had to disconnect or use another phone line to know whether the others were online, and so they discovered a need for a tool to find if somebody was online, and enable communication between connected users.
They weren't very finance-savvy, fortunately for them one of their parents was, and he handled all the fundraising and stuff.
All our email clients do is send it to our email servers. Try sending email out of your own machine. I doubt 10% would reach the destination inbox. The general assumption today is you don't run your own mail server. :(
How long ago was that exactly? From what I remember, ICQ had offline messaging around 1997.