I've played around with some vox software over the years and to make some words even close to understandable one must, as Chris said, play a bit with the words using spacing changes etc.
Using double vowels on some words helps a lot and double or even triple spacing between words can help. Remember English, as a language, is a bit funky at times an 'o' doesn't always sound like 'oh'... long and soft sounding vowels can be problematic. An 'a' doesn't always sound like 'a' but like an 'ah' etc etc.
True voice changers do work better if not taken to extremes, don't use echo or reverb, phasing etc because it just muddies the water...
As for remaining 'anonymous'... heh... don't kid yourself. A transmitter signal has a 'fingerprint'...
I remember the old days of SWLing... I could tune a receiver in the dark and listen to a dead carrier and know what SW station it was before they even sent the ID signal... I think some of you folks remember doing that yourself. Of course Radio Moscow had a dead give away sound to their carrier... yep... that awful hum on their signal gave them away every time...
Or Radio Habana's unique sound on certain transmitters they used... sounded kinda sorta like talking into a douche bag filled with wet cotton PLUS that Radio Moscow hum from those military surplus transmitters complete with a dynomotor whine that could be heard 50khz up and down the band...
Can you say carbon microphone?