Presenting three levels of progress toward the original monotheism of Abraham and all the prophets who were sent to enlighten and to warn the people of this planet.
The first step is when a Christian simply rejects the satanic Trinity concept that emerged by a vote in a meeting and at the same time accepts the final messenger Muhammad, thus accepting all prophets before him such as Moses and Jesus automatically. A Christian at this level may still hold on to the New Testament by objecting to some verses of the Qur'an. This is fine because the Qur'an only requires People of the Book to worship God alone. If they do not want to leave their own religious tradition and follow exclusively the way of the last prophet, his prayer and customs, then this is the minimum belief modification required to be saved on the Day of Judgment. I have to speak this harshly now because there is no excuse left for any Christian living in the modern world to have ignored the warning from Allah. Many have already discovered the oneness of God and a variety of Unitarian churches exist to support them, but more reform is waiting.
The second level is more emotional and involves a victory of the Qur'an over the Bible in authority which might take some time and careful study of the two. Here the cross is seen as the conspiratorial rumor that it really is and rejected, making Paul's whole theological blood fantasy collapse. Of the many Christian reform movements in history, none has ever managed to relinquish the crucifixion story, and I believe this is because only the truth in the Qur'an has enough power to break this ancient satanic symbol. The rare Christian on this level has taken full responsibility for his own actions - he needs no savior's blood - obedient to the actual words of Christ instead of what others made up about his life.
Finally, the Divine Sonship is abandoned, and Jesus the son of Mary is rightly placed on equal regard with all the prophets and messengers sent from the one and only transcendent God who created everything. How deep the father-god metaphor has burned their minds, but here on the third level a Christian is completely in line with the teachings of the Qur'an - on the true nature of God at least, and is now a believer in the purest form of monotheism available.
Abraham was neither Jewish nor Christian, but was upright, was submitting, and not from the polytheists. And if the People of the Book would only believe, it would be better for them. Allah speaks truth.