So VoIP can be better... at the expense of needing more bandwidth. During the session initialization the two VoIP endpoints handshake over which codecs will be used (kind of like the Accepts header in HTTP). Just like images, higher quality codecs tend to use more bandwidth (though like images its much more nuanced than that). Similarly like image formats there's different amounts of loss in the encoding/decoding of the voice data.
Voice has a major difference though. Its generally a real time protocol (its data packets are called RTP and sent over UDP generally). With images you can afford to wait longer for high quality images to load over a slow network. In a phone call that delay gets a bit annoying (to put it lightly).
Most people would rather trade quality for timeliness. You ISP would rather throttle your bandwidth and may not care about your quality (to a point).
Its quite a bit more complicated than that, but in a nutshell with VoIP, "higher quality" = "more bandwidth". If you don't have the bandwidth you'll have a very hard time getting better quality. If you have the bandwidth locally, then your provider or some network link along the way either doesn't have the aggregate capacity or may be actively throttling your rate to limit usage.
Voice has a major difference though. Its generally a real time protocol (its data packets are called RTP and sent over UDP generally). With images you can afford to wait longer for high quality images to load over a slow network. In a phone call that delay gets a bit annoying (to put it lightly).
Most people would rather trade quality for timeliness. You ISP would rather throttle your bandwidth and may not care about your quality (to a point).
Its quite a bit more complicated than that, but in a nutshell with VoIP, "higher quality" = "more bandwidth". If you don't have the bandwidth you'll have a very hard time getting better quality. If you have the bandwidth locally, then your provider or some network link along the way either doesn't have the aggregate capacity or may be actively throttling your rate to limit usage.