Earlier quoted context omitted.
It's this easy. http://youtu.be/NSC4Y8yA-jY
It's a very interesting talk but from what I saw that's not a terminal guidance package by any means. The antennas would need to be too big to fit into a missile. Also it doesn't work very well in an urban environment as the end of the talk shows. There's a huge difference between targeting the radar of an aircraft or a ship or a mobile SAM site and targeting a cell phone.
You don't need a complex guidance package when traditional direction finding and triangulation will produce coordinates that can be used to direct artillery, air strikes, IED, etc. Sigint targeting is quite common.