Are you listening comfortably?
The original bullet from Skype reads
"- improving audio bandwidth going from 8 kHz to 12 kHz" which is lazy-English for "Raising the upper frequency limit from 8kHz to 12kHz", .......... no mention of the lower end.
For any pedants watching, 8Hz lower limit would be a waste of engineering resource: there is an empirical "rule" which works quite nicely and is based loosely on what "sounds right". This states that the product of lower & upper frequency limits (actually more like -3dB points) should be 1E6, i.e.have a geometric mean of 1000 (so, 300 to 3400 is fine, as is 100 to 10kHz etc. etc.) If you flout this guidance big-time, things can sound quite odd, as you can sample by listening to a European AM station on Hi Fi speakers.
So, for the Most Satisfying Listening Experience, we'll settle for 80Hz-12kHz ta very much