Big differnece. There was no software installable on "dumb" telephones. They could not be programmed remotely to change functionality to listening without ringing. That would have required an easily detectable hardware change. Smart devices on the other hand are always vulnerable to this possibility.

Granted it took a bit more doing than nowadays, but the old phones had a mechanical ringer that is basically a microphone. No rewiring necessary. http://www.bugsweep.com/instrument.html and https://www.schneier.com/blog/archives/2010/01/eavesdropping...

Most of these new microphones do not have physical switches that can be off and still be useful, and most do not have networking that can be killed by unplugging.