Please see Mom's post from a little earlier today--I'm not trying to step on it...
I'm becoming more and more convinced that the "pains of hell" are guilt and regret felt by people who haven't accepted the atonement and repented of their sins. It seems that every few days I find something else in the Book of Mormon that makes this clear. Today I read,
"...and his soul began to be harrow up under a consciousness of his own guilt; yea, he began to be encircled about by the pains of hell." (Alma 14:6)
What were these pains? His guilt.
I think this understanding makes it clear why those who die "without the law"--those who are unaware that they are breaking commandments, including small children--aren't accountable for them. They don't have any remorse or regret, they feel no guilt for doing things that they never knew were wrong.
Again, this idea helps us understand the necessity of faith in Christ. When we are brought to be judged, we will recall all our guilt: "Wherefore, we shall have a perfect knowledge of all our guilt, and our uncleanness, and our nakedness...". (2 Nephi 9:14) This guilt will make us want to separate ourselves from God: "[Our words, works, and thoughts will condemn us...] and in this awful state we shall not dare to look up to our God; and we would fain be glad if we could command the rocks and the mountains to fall upon us to hide us from his presence.... [We must]... acknowledge to our everlasting shame that all his judgments are just." (Alma 12:14) We're commanded to prepare ourselves for judgement so that,"...[we] may not shrink with awful fear; that [we] may not remember [our] awful guilt in perfectness...". (2 Nephi 9:46) I'm not exactly sure how it will happen, but I'm inclined to think one of two or a combination of both things will happen:
1. As we repent in this life, our guilt is permanently removed. Enos experienced this, "I... knew that God could not lie; therefore, my guilt was swept away. And I said, 'Lord, how is it done?' And he said unto me: Because of thy faith in Christ..." (Enos 6-8) Alma the younger had a similar experience, "...I was racked with eternal torment, for my soul was harrowed up to the greatest degree and racked with all my sins. Yea, I did remember all my sins and iniquities, for which I was tormented with the pains of hell, ... yea ... the very thought of coming into the presence of my God did rack my soul with inexpressible horror. Oh, thought I , that I could be banished and become extinct both soul and body, that I might not be brought to stand in the presence of my God.... As I was thus racked with torment, while I was harrowed up by the memory of my many sins..." He recalled his father's teachings about Jesus Christ, and cried unto him for forgiveness, "...When I thought this, I could remember my pains no more; yeah, I was harrowed up by the memory of my sins no more." (Alma 36:12-19) With faith in Christ, we will not recall our guilt because true repentance will have removed that guilt from our minds.
2. I don't have much scriptural evidence for this one, but I'm inclined to think it's partly true. I believe, even those who have lived very righteously, will still feel guilty for things that they never repented of in this life (weaknesses they never overcame, sins they had forgotten from the past, sins they only then recognize for how bad they were). At that moment, Christ will say, "Father, behold the sufferings and death of him who did no sin...wherefore, Father, spare these my brethren that believe on my name." and "Come unto me, ye blessed of my father." I believe, when we hear those words spoken on our behalf and to us, our guilt will, again, be removed--provided we have faith in Christ.
There are other scriptures that support this view, though I'm not going to take the time to find them all now. If you have this in mind as you read the scriptures, I think you'll find lots of evidence, as I have.
As a closing, unjustified thought: People suffer the pains of hell in the spirit world prior to judgement in addition to (and not only) after the final judgement. The pains of hell, then, must not be physical pain because in the spirit world those experiencing them are disembodied spirits--no physical pain is possible.