This is some kind of Vietnam vets organization selling various things or taking straight donations.
They are using an older automated-dialing system. If you call (and don't get a busy signal), let it ring and ring until it picks up (it could take several minutes). You will then hear the system dialing a number. If you start saying, "Hello, hello" over and over, someone will come online thinking they have (auto) dialed someone else and that someone has answered the call. They will ask for Mr. or Mrs. whoever.
This is when you can have a little fun with them because they don't know who you are and you can be prepared ahead of time. Use your imagination!
It can make for some very funny recordings!