In addition to communicating with the local air traffic control facility, aircraft are required to give the Iranian Air Defense Radar (military) a ten minute 'heads up' that they will be transiting Iranian airspace.

This is a common procedure for commercial aircraft and involves giving them your call sign, transponder code, type aircraft, and points of origin and destination.

I just flew with a guy who overheard this conversation on the VHF Guard (emergency) frequency 121.5 MHz while flying from Europe to Dubai .

It's too good not to pass along. The conversation went something like this...

Air Defense Radar: 'Unknown aircraft at (location unknown), you are in Iranian airspace. Identify yourself.'

Aircraft: 'This is a United States aircraft. I am in Iraqi airspace.'

Air Defense Radar: 'You are in Iranian airspace. If you do not depart our airspace we will launch interceptor aircraft!' 

Aircraft: 'This is a United States FA-18 fighter. Send 'em up!' 

Air Defense Radar: (no response ... total silence) 

Thanks to Capt Cookie