As Javier mentioned, llamar para atrás (llamar pa'tras) is a literal translation of I'll call you back, and it is incorrect spanish, and outside of the USA, as José Miguel mentioned, the phrase has no sense.
Funny thing is when I've spoken to Puerto Ricans or Cubans who learned spanish in the USA, and I tell them, te llamaré de vuelta, and they try to correct me and tell me, "it is not de vuelta, se dice, te llamo para atrás." So I tell them, ah, gracias, que embarazo! :D