"Freedom of Speech" is a right endowed to us in the 1st Amendment to the Constitiution:
The 1st Amendment to the Constitutions
"Congress shall make no law respecting an establishment of religion, or prohibiting the free exercise thereof; or abridging the freedom of speech, or of the press; or the right of the people peaceably to assemble, and to petition the Government for a redress of grievances. "
The Declaration of Independence
..."We hold these truths to be self-evident, that all men are created equal, that they are endowed by their Creator with certain unalienable Rights, that among these are Life, Liberty and the pursuit of Happiness. — That to secure these rights, Governments are instituted among Men, deriving their just powers from the consent of the governed"...
Just thought I would add this one while I was at it, since it is almost Independence Day---July 4th.
The amendments are part of the constitution. They literally amend it. Freedom of speach is not in the articles, which are the original part of the constitution, but it was in the first amendment. The first 10 amendments are called the bill of rights and they were all passed together shortly after the constitution itself.