[gus_massa]

A little off topic, but this not standard additional features reminds me about fictitious features of the Martian Headsets models in http://www.joelonsoftware.com/items/2008/03/17.html

[rcfox]

His headset analogy is pretty accurate. It even goes one step further though: In China, some headsets have the mic and ground pin swapped. So before putting a signal on the mic line to see if it exists, you have to detect which pin is ground.