Random pointless phone calls

For the past three or four days now, between roughly 7:00 and 9:00 pm, I've been getting random phone calls, and the caller never leaves a message. Given that my answering machine message explicitly says "All of my calls are screened so please leave a message," one would think that if they really wanted to get in touch with me so badly they'd, oh I don't know, leave a message, maybe? If, however, they're just some telemarketer (even though I'm on the Do Not Call list)/charity/survey/whatever as I suspect, they need to just give it up, because it's not like if they try enough times that I'm suddenly going to decide to NOT wait for the answering machine to pick up the call. *sigh*