You can negate them as you say, yes. I think that most of the time, however, people use
will to guess who is there; they don't as often use
won't to declare who is probably not there!
Be
aware that many of the expressions you have been studying recently have
just one or two typical uses. It's all right to learn how to
negate them, how to
use them in the past, or how to form questions from them, but you need
to realize that not all of these forms are equally useful in real
conversations. 
CJ