Maybe this isn't considered 'online', but I used to play Warcraft (the original) with my brothers and friends split up in teams. Back then we had to do it using dial up through the phone, so we would dial each other and play. We would run back and forth to each other's house and talk smack in between games, good times ='). Phone calls used to interrupt our games and break the connection before we found out you could put a * or something before the phone number that would block any incoming calls.