There is something that I've wanted to know for a while now. So Valeris won't tell the names of her co-conspirators, so Spock uses a forcible mind-meld on her to get the names. Then Kirk asks for the location of the conference, so Spock digs deeper (which causes great distresses for them both). She doesn't know, so Kirk contacts Sulu, and he knows. Why didn't Captain Kirk or Spock just get in contact with Captain Sulu for those details?
If someone in the room might know the answer to a question, you usually ask them first before picking up the phone to call someone else. Really a better question is, why did Sulu know where the conference was? He wasn't involved in any way and they wanted to keep the location secret supposedly.