When Nik was asked to withdraw his name in place of another...It's obvious that he would choose Urvashi. This was their first attempt to get Urvashi a direct entrance to finals. And that is why the telephone was made to ring when niketan was closest to the booth.
When urvashi screwed up the task, bigboss gave this opportunity back to niketan because they did not want rajeev to be in finals and niketan was their 2nd choice of finalists.
I am editing and adding some more lines as people seem to have questions about the call -
It's very obvious sapna wouldnt pick the call because she herself had a chat with niketan that day over rajeev being so stupid in picking karishma's call and not niketan backing out the last minute.
Rest of the guys were at kitchen. Rajeev would no way repeat the blunder.
Believe it or not...Niketan was definitely expected to pick this call.