
We can look at table 1. that bandwidth consumption for classic voice call as same as G.711 VoIP call. It is because G711 VoIP call only converts a call to IP without do compression. We can tell that voice quality of G711 almost same like classic voice call. It make sense because there no data reduction at voice conversion. But, of course there is no point to use VoIP if we don't get benefit of it.
So, for sake of the benefit, almost all VoIP operator will chose codec other then G.711 codec. They want to reduce bandwidth consumptions for cost reason. At telecommunication business, that naturally selling the bandwidth, we can tell that more bandwidth consumption more expensive the cost, and less benefit for Telco company.
At other hand, they can not compress voice data to very minimum because consideration of quality. It always compromise between bandwidth and quality of VoIP Call. VoIP operators will choose the codec where the quality voice still acceptance by human hears. Base on my experience at VoIP call system, lot of operator choose G. 729 for theri VoIP codec.
It also can tell that almost all operators choose to use G. 729 codec. It is because G. 729 make lot of saving for bandwidth consumption. It is almost less 8 time then classic voice call (64 kbps). And quality of voice at G.729 codec still can tolerate by human hears. It is because there are some technique uses at G.729 codec to meet voice quality standard. But at some case, operators must use G.711 codec to compensate the poor link quality. G.711 more errors proof other than any VoIP codec.
I hope my explanation already can make you have more understanding about VoIP, especially according to Bandwidth related. Now, you can try to compare cost and quality of classic voice call then VoIP call by your self.