French has historically been the diplomatic language and the second language of the upper class in Persian circles, Iran is a class-conscious country. That said, I was there in a telecoms matter and that industry is of course dominated by English as the IT language. Add to that how Iran's youth is Anglo-Americanized just like all youth across the world (I noticed how Iranian girls have obviously taken Amy Winehouse as their role model in looks, the beehive is a way of making a fashion statement even under a headscarf) and that there are two English speaking Iranian dailies on sale everywhere. So English is today the dominant second language followed by French (spoken by older people) and even German (many younger Iranians studied and worked in Germany).
PS: I was only in Tehran.
PPS: I like Homeland as a series, but making a connection between Sunnite Al-Qaeda and Shiite Hisbollah (somewhere in the second season) was a real research howler. Those two groups hate each other's guts even more than they have disdain for the US and unlike Al-Qaeda it is Hisbollah's declared policy not to stage attacks on the US mainland (they do attack US military installations in the Mideast though). To them, the 9/11 attackers are not martyrs, but unislamic suicide killers doomed to go to hell.