都是陈述的语序!因为who是做主语,疑问句和陈述句的语序都一样.如果你要直接问,也是说：Who is calling?
第二个问题：
It is...to里,it 是后面to带的不定式的形式主语,比如It is important to learn English.
It is...for后面带人,对于.It is difficult for me to learn English.
It is...of 后面也带人,表示品性.It is kind of you to teach me English.