Skype shows "Virtual device" for Microphone, speakers and ringing

finally solved. I am running a 64-bit machine and a 32-bit Skype, so I just installed the libpulse 32 bit version:

sudo apt-get install libpulse0:i386 is all what was needed to solve the problem

I had your problem as well and solved it by installing pulseaudio and it's dependencies (packages paprefs, pavucontrol, pavumeter are not necessary, at least Skype works without them). I restarted Skype, and now it lists "PulseAudio Server (local)" for microphone, speaker and ring tone. Seems like a missing dependency in the skype package.

In my case, the reason is that I don't use PulseAudio and "as of version 4.3, the ALSA sound system is no longer supported without PulseAudio" (source)