We actually have an odd arrangement where I work. I take the loan apps and give out the loans. If the loans get to be delinquent, I call them up until they're 30 days past-due. Then I hand them off to our collector. He works them until they're over 90 and then hands them back to me to figure out what we should do with them, be it lawsuits, repos, etc.
We don't have an automatic dialer or computer system making our calls for us, so we can usually tell who is answering the phone and who the number belongs to. I have lot's of times where the customers give us their mom's house number when they get a loan, or they give us a friends cell phone # to call them on. If I know that someone other than the customer is answering the phone, we don't go into details about the debt. Common sense, if you ask me...
But yes, the computerized part of it does take out that factor of being able to tell who actually answers. I've only heard the automated calls that leave a phone # and maybe a reference number. I have yet to hear a computer going into details about the balance or anything else. Not that I'm saying it's not possible. I would think it is a little unethical in that the machine does not know who it's releasing information to and, if it is calling a wrong number, it has know way of knowing.
Now, regarding the cease & desist letter... I think that it would need to be presented in writing for it to be effective. The text of the fdcpa also states this:

Keep in mind, though, the FDCPA only applies to collection agencies, not to the original creditor. Sending a c&d letter to your creditor will have no legal effect. I have actually had a few customers send me c&d letters, and in it they quote the FDCPA and threaten to sue me if I ever call them again. I usually write a letter back and say "Since you seem to be well-read on our laws, please re-read the beginning definitions set forth in 1692a and you will clearly see that by definition of a debt collector, I am not."