Quote Originally Posted by dale View Post
My textbook translates "If we have time tomorrow, we'll phone (our) friends" as "Если завтра у нас будет время (завтра), мы позвоним (нашим) друзьям."

Why is it "у нас будет" instead of "у нас будем"?Thanks!
Because "У нас будет время" is 3rd person singular (the subject is "время"). You can rephrase it in more-English way: "время будет у нас" - "time will be at us (at our possession)".

Quote Originally Posted by dale View Post
When would you use "у нас будем"?
Never.