I can't even imagine there is a valid legal argument.
If somebody calls me, I can say whatever I want. If I want to answer the phone by saying "Department of Defense, how can I help you?" the First Amendment guarantees me the right to do that.
Now, I certainly could not call other people and claim to be the Department of Defense. That's fraud. The same applies if I had done something like put up flyers claiming my phone number was related to the DoD or something like that.
If somebody calls me, I can say whatever I want. If I want to answer the phone by saying "Department of Defense, how can I help you?" the First Amendment guarantees me the right to do that.
Now, I certainly could not call other people and claim to be the Department of Defense. That's fraud. The same applies if I had done something like put up flyers claiming my phone number was related to the DoD or something like that.
I'm not a lawyer, but that's how I see it.