Deut. 18:9ff. Dead people; people who have died; people who have bit the dust; people who have expired, given up the ghost. Of course, their souls live on...but the commandment is not to call them up. Obey the word of the Lord! He has His reasons.
Nobody is "conjuring" up anyone. We are merely imploring our friends for their assistance. Now if you think they are "dead" dead and "waiting" for the resurrection to occur that is one argument to make. I believe that God, being timeless, is with the Resurrected today. Whatever "today" means to God.
SD
Second, in asking the intercessions of the saints who are alive in Christ the Orthodox do not "call them up" (we are not trying to get a ghost to appear) nor do we engage in divination (we don't expect the saint to tell us the future, just pray with us to God).