The Russian S-300 family of missiles have become a key component in the Iranian plan to protect their nuclear weapons production facilities from attack from Israel.
Since it is a major issue, let's take a look at the missiles themselves: SA-10 Grumble, SA-12 Giant and SA-20 Gargoyle. They're long range surface-to-air missiles produced by Russia and are considered to be one of, if not THE most potent anti-aircraft missile in the field. The S-400 family of missiles (SA-21) are not yet deployed but are in production and are expected to be even more capable, but nobody expects Russia to sell them to Iran. However they may not need to in order to effectively shield the Iranian nuclear material production.
Having done a bit of research on the issue, I can't figure out how many of these SAM's Iran has. Libya may have sold some of their S-300's to Iran and the Iranians have been trying to buy up whatever they can lay their hands on including inventory from Belarus and Crotian arsenals.
The Israeli jets may not get as far as Iran though. Former Democratic US National Security Advisor Brzezinski suggested that the US would shoot down the aircraft of its ally, Israel. (CLICK HERE)
The situation for Israel is becoming increasingly perilous and the stakes have been raised by Dear Leader, who, as a Muslim (former Muslim by some accounts), has no love for Israel.