According to this from February 10, 2006 http://www.rferl.org/featuresarticle/2006/02/f1477c44-4533-4436-b19d-1948ed806ce2.html “Reports that Iran two years ago acquired two S-300 batteries that have been deployed near Tehran remain unconfirmed to this date.”
But, this is from December 28, 2007, i.e. yesterday:
“RUSSIA SAYS IT IS HELPING IRAN STRENGTHEN AIR DEFENSES
Deputy Foreign Minister Losyukov said on December 27 that Russia is helping Iran strengthen its air defense capabilities, RIA Novosti reported. “I know we are assisting in work to reinforce Iran’s air defense systems,” Losyukov told reporters in Moscow, adding, however, “I have no concrete information on the issue and can make no comment whatsoever on the type of [military] hardware.” Iranian Defense Minister Mostafa Mohammad-Najjar said on December 26 that Russia will supply Iran with the S-300 antiaircraft missile-defense system “on the basis of a contract signed with Russia in the past,” but did not say when or how many of the systems will be shipped to Iran. Russian officials declined to comment on the S-300 sale (see “RFE/RL Newsline,” December 27, 2007). Meanwhile, the Bush administration expressed concern over Iran’s announcement that Russia will supply it with S-300 antiaircraft missile-defense systems, AFP reported. “We have ongoing concerns about the prospective sale of such weapons to Iran and other countries of concern,” said Scott Stanzel, a White House spokesman. JB”
http://www.rferl.org/newsline/2007/12/281207.asp
So, we better update the threat list.
Opinion only:
Russia would be silly to miss the chance to combat test the S-300, and I suspect there’s at least couple launchers and a C&C trailer somewhere in Iran, probably under “joint” control.
Most of the modern AD components benefit greatly from a nationwide integrated air defense system, which to my best information, Iran does not have. This would limit the effectiveness of any S-300 systems deployed in Iran, even if Russia supplemented their early warning network with national technical support.
One or two missile systems are one thing, but hiding large shipments of same, as well as the deloyment preparations, and crew training exercises, these are much harder to conceal. The minute you light one of these systems up, odds are somebody watching close will notice.
Best guess says Iran has a very few S-300s, but not many, and not part of a larger IADS.