MCI-Worldcom are the most recent offenders, calling me two nights in a row at the same time last week. The first night I told the guy that I wasn't interested, that it was after 8 pm and I just wanted to relax and not think about long distance. So he says, "Well I think if you're relaxing, that's a perfect time to talk about long distance..." I grew angry, told him the conversation was over, and hung up.
The next night, a woman from MCI-Worldcom called with a similar pitch. I immediately told her I didn't want to talk about long distance and that I had a bad experience with her comrade the previous night at that time. She takes this as a cue to be more aggressive, telling me that she is calling to raise my rates and how does that sound? I come to my senses and tell her I'd like to be removed from their list, to which she responds that if I will hear her out, she will never call again (someone doesn't catch on very quickly...). I tell her to remove me and terminate the call.
I say all that to say this: if you answer the phone, say hello, and don't get an immediate response, hang up. It's a telemarketer. The only way those MCI-Worldcom bastards got through is by calling back after I did that, which just goes down as further proof that they are evil incarnate.
As if I needed more proof.