Is "Ils ont" and "Ils sont" pronounced the same way?
Due to "o" being vowel, we link them to sound better, while in the other, the "s" is silent, right?
When a -s makes a liaison, it makes a soft /z/ sound, which is distinct from the hard /s/ sound at the begining of sont:
'Ils ont' is /ilz_õ/ while 'ils sont' is /il sõ/
In casual speech it's common to drop the l sound, but the laison remains, giving /izõ/ and /isõ/