The words "I want" and "I fly" are both volō. Was there ever any difference in pronunciation in the classical era or later? I expect such differences to be more likely in vulgar Latin. The rest of the forms of these two words differ, so the question only concerns this particular form.
This question arises from Italian, where the two forms are voglio and volo. This -gli- instead of -l- may well be due to interference with other forms of the irregular verb, but it could also be a reflex of a difference that developed within Latin. If there is no such difference, then the distinction must be a Romance or Italian invention. I am not aware of any differences in pronunciation between the two volō's, but I've been surprised before.