The other day, my good friend Mike Chambers mentioned that he was planning on building a closed-circuit phone system as a toy for his kids. Since my kids already think his pancakes and popcorn are better than mine, I decided to beat him to it. It turns out that creating a simple closed-circuit system is extremely easy, and can be done for just a few dollars in parts (especially if you already have a couple old disused phones lying around).
As I was wiring the whole thing up, it occurred to me that building your own private phone line would be an effective (if slightly inelegant) way to ensure that your point-to-point electronic voice communication wasn't being intercepted by the NSA. You'd probably want something more robust than a few 9 volt batteries, a resistor, and some electrical tape, but it wouldn't take much more work or money to build something fairly serviceable for a small number of endpoints in relatively close geographic proximity.
I'm certainly not one to advocate using a system like this to break the law, but I am a proponent of civil liberties, and I do feel strongly that citizens of all nations have a right to communicate freely without being spied on by their own governments. The gradual erosion of American civil liberties is a major theme of my new novel Kingmaker which has recently become much more realistic than even I anticipated.