Your voice is fading in and out.
→    당신목소리가 들렸다 안들렸다해요.

[예문]
A:Mom, where are you?
  엄마 어디세요?

B: I'm on my way to the home. What's up?
  집에가는길이야.무슨일이야?

A:Mom, I can't hear you very well. Your voice is fading in and out.
  엄마, 잘안들려요. 목소리가 들렸다 안 들렸다 해요.

B: That's because I'm in a tunnel right now. (Beep) Hello? Hello?
   지금터널안에있어서그래.(삐)여보세요?여보세요?