Most of these friends have been from the same college as me, but we used to have a forum set up and I started talking to a few guys on there. Got started going down to the LAN parties that one set up and we've been great friends ever since.
There is one good friend I have who lives on the other side of the country who I met online from a music forum. I've met her IRL a few times, but we mostly converse via letters and twitter.
So friends online are possible. I speak to Joonas from here a lot as well.