In the past two days alone, I've gotten over 20 spam calls with none of them leaving a message. Just 3/4 seconds of silence on my voice mail. One call the other day left a 22 second blank message.
I do this all the time too. The new standard for polite calling anyone is to initiate the conversation if the line goes live as far as I am concerned. Never say anything for an unknown caller, and expect to get dropped or hung up on even if you are legitimate. If you're unwilling to call me twice or thrice, you didn't need to call me in the first place.