[lucaspiller]

There are good quality codecs available that use less bandwidth and have better quality than traditional phone calls, but they are encumbered by patents and license fees. Most people just care about getting a service cheaply/free rather than the actual quality, so most providers will just use the G711 (what landline phones use for trunking) or GSM codecs which are free to use. G722.2 (AMR-WB or "HD Audio") provides a better quality at less than half the bandwidth of G711, but it isn't free to use so very few providers support it.

Not only that, but the codec needs to be supported at all stages of the call (the phones, the VOIP server, the trunk if external, etc), and if not it'll need to be re-encoded, which uses more CPU and reduces the call quality. As such you are probably better off just sticking with a more common, lower quality, codec. It's a chicken and the egg problem as providers won't support more codecs until hardware does and vice-versa (Twilio's SIP trunking service only supports G711, which is kind of the lowest-of-the-low).