When Kurisu asked Okabe if he is ready, he will type something but just don't send the text. Then he will type something in his second text so just send the text, and you will unlock the route of Feiris.
I got all the 6 routes: Ruka, Feiris, Moeka and Kurisu route are easy to get.
Except for Mayuri & Suzuha. I don't know how bout just lucky to get their route. I think something to do with sending the text. --- I am "The God of Conquest" Currently Playing: Resident Evil Operation Raccoon City "PS3"