Well, he is definitely right! Kibbits had a dark vocal sac underneath. So, if your frogs have that, that's a pretty good indication. He may not be quite ready yet : )

I remember that when Kibbits first started out, it sounded like little chirps, and then progressed into an actual call, and as he got older (just like teenage boys!), his voice got lower!

I can't wait to hear your frogs little voice! You should definitely record it and share once he does!