From a person that has studied the Quran, yes, that is a fact as found in Quranic verses.
"If Allah so willed, He would have made you a single People, but His plan is to test each of you separately, in what He has given to each of you: so strive in all virtues as in you are in a race. The goal of all of you is to Allah. It is He that will show you the truth of the matters in which ye dispute." (5:48)
"Say, 'O People of the Scripture, come to a word that is equitable between us and you - that we will not worship except Allah and not associate anything with Him and not take one another as lords instead of Allah .' But if they turn away, then say, 'Bear witness that we are Muslims [submitting to God].'" (3:64)
"And do not argue with the People of the Scripture except in a way that is best, except for those who commit injustice among them, and say, 'We believe in that which has been revealed to us and revealed to you. And our God and your God is one; and we are Muslims [in submission] to Him.'" (29:46)
"There shall be no compulsion in [acceptance of] the religion. The right course has become clear from the wrong. So whoever disbelieves in Taghut and believes in Allah has grasped the most trustworthy handhold with no break in it. And Allah is Hearing and Knowing." (2:256)
It lets religious pluralism and the right for people to think what they want and say what they wish, at least in terms of faith. It might be considered blasphemy to say "I disbelieve in Quran, God and Islam" for the Muslims, but the Quran clearly says in the chapter "The Infidels," that the infidels has the right to say it.
I also think there is a letter (or Hadith) written by his companions attributed to Muhammad, it was originally sent to the Saint Catherine Monastery;
- This is a message from Mohamed ibn Abdullah, as a covenant to those who adopt Christianity, near and far, we are with them.
- Verily I, the servants, the helpers, and my followers defend them, because Christians are my citizens; and by Allah! I hold out against anything that displeases them.
- No compulsion is to be on them.
- Neither are their judges to be removed from their jobs nor their monks from their monasteries.
- No one is to destroy a house of their religion, to damage it, or to carry anything from it to the Muslims' houses.
- Should anyone take any of these, he would spoil God's covenant and disobey His Prophet. Verily, they are my allies and have my secure charter against all that they hate.
- No one is to force them to travel or to oblige them to fight.
- The Muslims are to fight for them.
- If a female Christian is married to a Muslim, it is not to take place without her approval. She is not to be prevented from visiting her church to pray.
- Their churches are to be respected. They are neither to be prevented from repairing them nor the sacredness of their covenants.
- No one of the nation (Muslims) is to disobey the covenant till the Last Day (The end of the world - Judgement day.).
Regarding its authenticity, some say that since it's a copy of an alleged original version that never was subject to examination by other scholars than those specifically chosen by the authority (thus suspected by some to have been under duress in their confirmation or unreliable, schematic scholars), some critics have pointed this out to dismiss it, but it more or less doesn't affect the authenticity of the letter, the original version was held by people that aren't suspected to deceptive, to believe it was altered is mere wishful thinking, pure conjecture and there is no credible sources in support of this claim. Though, since it's only a copy of an alleged original that has since then been destroyed, we are not to say this letter is conclusively authentic or true either, allege doesn't necessarily mean false and doesn't necessarily mean true, therefore there is no way to actually determine its authenticity.
It falls under the classification of a "maybe," "inconclusive." It may and it may not be true. No way to actually tell other than to speculate for yourself and assert your own opinion on this subjective matter. If it's authentic, it is furthermore proof of Islam teaches free speech upon those already sufficient enough evidence from the Quran. If it's inauthentic, then we can either say that most Muslims still has regarded it as reliable and incorporated it into their doctrine of Sunnah, but the Quranic verses should be plenty and enough if it's inauthentic. Two responses, Trinity, a Roman-founded doctrine, did not exist during the Islamic era, at that time Christians were Unitarians, a Levant-founded doctrine. Trinity did not exist and was not founded until many centuries after Islam and more than a millennium after Christianity's establishment. Islam criticizes the earlier, Unitarian Son of God doctrine, which is claimed to be the earliest doctrine of Christianity after, in Islamic belief, the corruption of the original Christian teachings of Jesus Christ, but even there, the answer is no. I'm not going to answer these questions directly, but an indirect response to give you an insight, none of that asked are Islamic doctrines, but Muslim opinions, more or less, with high status (whether by Sunni scholars or believers in general).
The conclusion is Islam believes in free speech.