I'm assuming the debt is your's and they're trying to get information about you from him? I've been told you can try sending a letter to them called a limited cease and desist. Actually, if it is your debt and they are calling him, he has the right to tell them to stop calling him and if they don't, he can sue for harrassment. If the debt is yours, he doesn't owe them anything, including talking to them on the phone. He can tell them not to call him again and hang up the phone. If they call back, he can press charges.
Just my two cents.
Kristina