If a person shouts at you in the street that you are a wretched of a human being and do not deserve to be where you are, is that considered an instance of Free Speech? My personal answer would be "yes!" What if you are sitting in your seat at a discussion conference on "economic prosperity and its effects on civil society" (a made-up title, of course) where people are to ask questions from a panel or a speaker, and the same thing happens? My answer would still be "yes!" I guess there is little place for disagreement on this affirmative answer, as it derives from a quite basic understanding of Free Speech.
What if the police or the security personnel ask the person to be quiet or demand that s/he leaves in each case: should they have the right to do so in a free society where Free Speech is the rule? My answer would be "no!" in the first case, and "yes!" in the second. The reason why I think so has nothing to do with Free Speech per se, but the purpose of each gathering. In the first case you are not in the street to serve any particular purpose; you are there just because you are a member of the reference society you live in, and the person who shouts at you is there since s/he is also a member of the same society. In the second case, however, you are at the conference to "discuss" the topic of the conference. Your very presence means you have accepted that as a rule. The security is there, too, to enforce that rule. So, if someone starts shouting at you, although s/he is free to do so, per the rule of Free Speech, the security has a responsibility to deal with the shouting person, for the conference to go on towards its goal as set by its topic and practice.
So, what kind of Free Speech is it then that the speaker would be effectively silenced, one might ask? The way Free Speech is implemented in free societies is rather simple, yet perhaps subtle. The reason it is subtle is that:
Free Speech is for everyone, i.e. all people should be free to speak their minds. Thus, in response to the first person who is shouting, the person who is shouted at also has a right to respond, or perhaps shout back. If that is what actually takes place, the purpose of the gathering/session/environment would be violated and the reason for which it is created undermined. That is where Free Speech should be regulated itself (not blocked or removed, I must emphasise) through two simple rules:
A. One is free to speak her/his mind according to the rule of Free Speech; yet the creators of the "environment" in which the Speech is made are also free to set regulations on the content of the Speech or the manner in which the Speech is made. They may assign regulators, who have "the right" to enforce these regulations after the Speech is made, not before—that is Free Speech should take precedence to any regulation of this sort no matter what environment.
B. The "reference environment" that is formed by the union of all such "environments" should be free of such regulations as regards Free Speech. Thus, the regulations of the sub-environments of the reference environment cannot take the form of trial or result in any sort of prosecution, criminal or otherwise.
Note that rule B is meant to prevent abuse/misuse of rule A, that is blocking or constraining Free Speech essentially and fundamentally with the excuse of higher-level regulations and/or higher moral grounds. In the body of rule A itself, the precedence of Free Speech over what regulates it in (sub-)environments (of the reference environment) is underscored.
I should like to draw some examples where it would be clear why these two rules are necessary and enough to ensure a meaningful implementation of Free Speech:
First let us consider a country. The reference environment is clearly the country itself, including its public places. Everyone should be free (by law or common law) to express their mind in spoken or written words or signs. That automatically results in the Freedom of Expression, Freedom of Press, Freedom of Gathering, and a host of fundamental rights. These are all inter-related and derive from the same principle; see, for instance, Bill of Rights, Amendment I, and some related annotations. That's what is practiced in the free world, say the US or Canada, and what the rest of the world, say Iran, lacks. However, once a group or an individual sets up, say, a newspaper, they are free to set regulations on what they publish. They do not need to publish every single line of e-mail or letter or phone call they receive. No one really expects New York Times to publish whatever one writes to them. A newspaper is created for a purpose, and its content is regulated per that purpose.
The same holds true for a web site, as an environment with expressed goals and regulating rules. The example of a web site is especially important since the web, by structure, is interactive and publishing online material has become increasingly easy, so much so that it is now instant. It is similar to speaking in a 10-by-10-meter conference room. Everyone can hear you the instant you talk. So, if I burst out in fire-rapid comments against the tyranny of clerics in Iran in a gathering room on "Scientific advancements of the Iranian society" I should not be surprised if I am asked to be silent or leave the room, or directed to another room on "The future of theocracy in Iran," a more proper topic on which to make my commentary.
As another example and to summarize: Michael Moore shouted "Same on You, Mr. Bush!" in last year's Academy Awards ceremony. I do not agree with him, but he had every right to do so as an American citizen and yet he was not given more than one minute for his speech by the organisers: he surely could not demand more time, instead he publishes books, makes films, and runs a web site where he could be heard very clearly. I take it as granted that the US is a free country, and leave it as an exercise to see that the rules I described were all followed in this case, especially the existance of the regulations and the lack of any prosecution afterwards.