VoIP is nothing else than a new alphabet.

The letters of our alphabet are derived from a script invented, or at least developed, by the Phoenicians.
Their neighbours, the ancient Greeks, adopted this for their own use and by translating Phoenicians letters into Greek, gave the world the alphabet.

The Greeks were probably the first to marry writing with speech.
Originally they didn't separate words, then, to help pronunciation, they invented the vowels and used spaces to separate words.
Successive cultures chopped and changed the alphabet, by amending, adding and dropping letters to accommodate differing glitches and sounds. With 26 characters (but the Italians still just use 21) 403,000,000,000,000,000,000,000,000 pronounceable words are possible.

All characters were originally signs and all signs were once images.

VoIP is just another kind of alphabet.
The letters are numbers and the codec puts together the numbers and recreate the voice.

From that the importance to use the right codec and the right protocol.
The quality can change enormously depending on them.

If you want to be clear, just use the right "alphabet".