1.答案：We won't tell anyone about your call (unless) you want (to).
2.
1）根据从句句意中的“如果不”,所以从句的引导词是unless；
2）第二空采用了不定式的省略,即want to = want to (tell anyone about your call).括号中成分主句中已经含有,为避免重复,所以省略.