Answers... hopefully

Mike posted this comment and i thought it would be good to try to answer his question for him.

Ok, strange question. You're confident that Jesus Christ spoke with God and is his last true prophet, right?
Why do you think devout believers of another religon disagree? I'm especially curious about the ones who spoke with God after Jesus, such as muslims, and mormans.

This is not a question that has a simple answer. Especially in the limited space available here. So i will try to answer as best i can in the space i have. First, the Bible makes it clear that Jesus the Christ (Messiah) is not just another prophet. This is made clear in the Old Testament a.k.a. the Jewish scriptures. Let me go through a series of scriptures to deal with this. (I am aware that the Jewish Scriptures have chapter and verse divisions that are not exactly the same as the Old Testament Bible, however the content is the same) . Most of the beginning of this list is basic principles...

1) God is Holy - Leviticus 19:2 Speak to all the congregation of the sons of Israel and say to them, You shall be holy, for I, Jehovah your God, am holy.
2) Man is a sinner - Isaiah 64:6 But we are all like an unclean thing, and all our righteousnesses are like filthy rags; We all fade as a leaf; and our iniquities, like the wind, have taken us away.
3) Sin separates man from God - Isaiah 59:2 But your iniquities have come between you and your God, and your sins have hidden His face from you, from hearing.
4) Attonement is through blood sacrifice - Leviticus 17:11 For the life of the flesh is in the blood. And I have given it to you on the altar to make an atonement for your souls. For it is the blood that makes an atonement for the soul.
5) Complete or true attonement is only available through the Messiah's sacrificial death - Isaiah 50:5-9 and Isaiah 52:13-53:12
6) The Messiah had to have already come - Daniel 9:25-26 Know therefore and understand, that from the going out of the command to restore and to build Jerusalem, to Messiah the Prince, shall be seven weeks, and sixty-two weeks. The street shall be built again, and the wall, even in times of affliction. And after sixty-two weeks Messiah shall be cut off, but not for Himself. And the people of the ruler who shall come shall destroy the city and the sanctuary. And the end of it shall be with the flood, and ruins are determined, until the end shall be war.
- 7 weeks is 7 7's or 49 - the city of Jerusalem was rebuilt in 49 years. 62 7's is 434 years after that that the Messiah was supposed to have been cut off (killed) but not for himself.
7) Jewish Messiah is required for the salvation of both the Jew and the Gentile - Isaiah 42:6 I Jehovah have called You in righteousness, and will hold Your hand, and will keep You, and give You for a covenant of the people, for a Light of the nations;
8) The Messiah is eternal - Micah 5:2 And you, Bethlehem Ephratah, you being least among the thousands of Judah, out of you He shall come forth to Me, to become Ruler in Israel, He whose goings forth have been from of old, from the days of eternity.

There are many, many, many, many other prophesies concerning the Messiah/Savior showing that he would be more than just a prophet. I found this website that covers many of the prophesies concerning the coming and fullfillment of the Messiah.

What does all of this have to do with Islam and Mormanism? Simple. These religions treat the Christ as if he is simply another prophet and his coming, death, and resurrection was not the completion/fulfillment of the law that the old testament (Jewish scriptures) and new testament show that he is. Their added "scriptures" are attempts to "complete" by addition what has already been completed. As Revelation 22:18-19 states; For I testify together to everyone who hears the Words of the prophecy of this Book: If anyone adds to these things, God will add on him the plagues that have been written in this Book. And if anyone takes away from the Words of the Book of this prophecy, God will take away his part out of the Book of Life, and out of the holy city, and from the things which have been written in this Book.

As i said, this is a limited explanation and does not even come close to fully answering your question, but under the circustances and time & space limitations, this is the best i could do.