What requirements are needed to fly an approach that requires you to fly over the US/Mexico border? I was flying North of El Paso Texas listening to El Paso Approach when I heard Approach ask a Falcon Jet if they could fly into Mexico to fly a Runway 4 GPS approach.  At El Paso, the runway 4 approaches require you to fly across the US/Mexico border into Mexico.  What requirements are needed to fly an instrument approach that requires you to fly over Mexico?  Would you require a radio telephone permit to use the radio even though you are talking to an FAA controller?
I had flown my plane (small 4-seater) from Houston to California a few years ago and on the way back, I stopped in El Paso to refuel and sleep for the night.  While in contact with the tower, following whatever vectors they were giving me, I noticed that I was about to cross into Mexico.  It's pretty obvious from the style of buildings and how close they are together that one area is Mexico and the other area is the US, especially at 1000 ft (or less) AGL.  I asked the controller if this was correct since it would put me across the border into Mexico.  I seem to remember him saying something about they had an agreement with Mexico that allowed them to use / control that airspace.