Yep I get that, do you have any issues with carrier sync?, I spose a few hz drift and resultant pitch change isnt going to be so bad.
Transmitting some carrier also makes it harder to eaves drop, and the pll totally cancels it in the decoder.
I knocked togther a circuit on breadboard, not a decoder just an encoder, a 555 and '602, yes it makes a right mess of speech, I dont think lorry drivers and bosses would be able to tell we are calling them names over the air.
I spose if I were to record the scrambled audio then played it back through it would descramble.