helpformyson: I too have a young adult addict son. I can only tell you some of the inklings i've learned along the way.
I too would wonder if it is my place to call back and relate this kind of information. I've learned that with people who are not in recovery with me, with any message I give I can somehow get blamed for whatever decisions my son has made. Especially if the request comes from people who distanced from me to begin with. I can just imagine my ex-inlaws using any kind of response from me as the gossip-of-the-week material.
If i had a message like that on my machine, i too would ponder on how to respond. Ignore it totally? Call back with some very vague details about the addict? What if this aunt had called and I was home - would I ignore the name when i saw it on the caller ID? I don't know, i guess (because this came from the family that had estranged me) i would just ignore the message. This aunt is not calling with a desire to help you son nor is she calling to say she has herself gotten involved in Alanon. She is just calling for the latest stuff.
One of the things I try to use as a guide is whether I am creating undue tentacles for my son to have to deal with when the time comes that he chooses to be clean, sober, and in recovery. I try not to give details about his life that he might not want other people to know.
That's my random thoughts. Hope it helps.
Sojourner