Ok, this was a voicemail message someone just left me at work but I immediately thought of this thread.
"Hi, this is Michael from x. I'd like to speak to you about y. You can call us back through the website."
Guess who's not getting a call back.
If he can't be bothered to leave a phone number, then I really can't be bothered following up.
Also, this is how I imagine that scenario would unfold: I Google them to find the website, find the contact details, call the number, get through to a switchboard, ask to speak to Michael, and get asked "Michael who?" ... no idea. End of treasure hunt.
Edited for grammar.