I can confirm that the stuttering issues I have experienced where the person I call cannot hear me or hears everything choppy/stuttering, is due to the quality of the 3G connection.
I used the echo number posted again today, and made several calls via wifi with zero issues, crystal clear quality.
I then switched to 3G, and made a long call to the echo number rather than hang up 10-15 seconds after hearing stuttering. I found that the stuttering would get worse, then better, back and forth, but never go away completely. This was over a 5 minute test call. The stuttering ranged from bad but you could still kinda understand what was being said, to so bad you couldn't string together a recognizeable sentence. At times the delay was less than a half second, others it was over 2 seconds. Checking the Outgoing Audio Processing box did improve things a bit, but not enough to make things understandable when the stuttering was bad or the delay was long.
BTW- I get poor 3G at home, so I run a hybrid PRL which seems to have me tower hopping alot at home, according to the OpenSignal app.
Funny BTW- Once sentence I said while testing with the echo number was
"This seems to go from bad to good to bad and back again."
What I heard was
"...seems ...go ... om bad... to bad... again."
Love the app, glad I bought it, works great when I have a good signal over wifi, just wish I could get good calls over 3G as well.