As another representative of early Jewish appraisal of 1 Samuel 28, here is what can be found in Sirach (second century BC) about it:
"Before the time of his eternal sleep, Samuel bore witness before the Lord and his anointed: 'No property, not so much as a pair of shoes, have I taken from anyone!' And no one accused him. Even after he had fallen asleep, he prophesied and made known to the king his death, and lifted up his voice from the ground in prophecy, to blot out the wickedness of the people." (Sirach 46:19-20).
Justin Martyr (second century AD) concurred. The idea that it wasn't Samuel but a demon that spoke was first attested in the third century AD. There is a book that contains the original texts of the discussion of this topic called The "Belly-Myther" of Endor: Interpretations of 1 Kingdoms 28 in the Early Church (BSL, 2007). Here is some of what Origen wrote about this topic:
"We know very well that some of our brothers look askance at the Scripture and say: 'I do not believe the medium; when the medium says that she had seen Samuel, she lies. Samuel was not summoned. Samuel does not speak. Just as there are false prophets who say 'Thus says the Lord' and the Lord has not spoken, so this petty demon is lying when it promises to bring up the man Saul asked for, saying, 'Whom shall I summon for you?' when he says, 'Summon Samuel for me.' This is what is said by those who say that this story is not true: 'Samuel in Hades? Summoned by a necromancer? Samuel, the exceptional prophet, who was devoted to God from birth, who from before his birth was destined to be in the Temple, who had worn the ephod since he was weaned and had been invested with double mantle as priest of the Lord, to whom even as an infant, the Lord spoke oracularly?' .... These things are what they say, those who do not want to accept the struggle of explaining how Samuel was summoned. But since one must remain faithful in heeding the Scriptures, since the matter has been bruited about and can really annoy and disturb us, let us see whether or not the person who does not accept the Scripture ever understood it or whether, undertaking his interpretation with good intensions, he speaks the opposite of what is written.
"What then does the necromancer do to summon the soul of a just person? This is what the earlier argument sought to avoid. For, so as not to experience the struggle concerning so many other matters that might be investigated in this place, it says: 'It is not Samuel, the demon is lying, since Scripture cannot lie.' But these are the words of Scripture, they are not from the persona of the so-called demon itself, but from Scripture's persona: 'And the woman saw Samuel' and 'Samuel said' what was said by Samuel. This is what Scripture says. How, then, can we present a real solution to the necromancer's behavior in the first place? I ask the person mentioned earlier who upheld the argument 'Samuel in Hades?' and so on that he answer this question: Who is better, Samuel or Jesus Christ? Who is better, the prophets or Jesus Christ? Who is better, Abraham or Jesus Christ? Here no one who has once come to know that Jesus Christ is the Lord previously prophesied by the prophets will dare say that Christ is not better than the prophets. Therefore when you confess that Jesus Christ is better, did Christ come to be in Hades or did he not? Is it not true what was said in the Psalms, interpreted by the apostles in their Acts as referring to the Savior's descent to Hades? .... And I ask: 'Did they prophesy supercelestial things?' Is a little demon capable of prophesying concerning the entire people of God that the Lord was about the deliver Israel? Can also a little demon know this, that after a king has been appointed with the anointing oil of a prophet that tomorrow Saul and his sons with him will forfeit their lives? For my part, I cannot allow a demon such great power as to prophesy concerning Saul and the people of God, and to prophesy about David's kingship that he was about to reign."
And on whether Saul really died the next day, here is the interesting comment by Diodore of Tarsus (fourth century AD):
"Some think a demon appeared in the form of Samuel and conversed with Saul. I do not think this is right. For God would not have permitted the deception to take place in the form of Samuel. Nevertheless they do have something by way of a counter-argument. For they say it is proved that the demon is lying by what it says to Saul, 'Tomorrow you and Jonathan will be with me', since what he said did not happen the next day but on the third day. But they have stumbled far from the truth. For it would not be possible to prove that Saul died on the third day after Samuel's words, since what follows in the narrative is a resumption of the entire course of events and of the war. For divine scripture did not say that Saul died 'on the third day' after the belly-myther spoke. Rather, after telling the story of Saul's error and of Samuel's pronouncement against him, it takes up the account again from the beginning.... Also where did the demon get the idea that not only Saul would be killed but also Jonathan?"