This # calls at least 2 - 3 times a day.  When answer machine picks up they don't leave a message.  I finally got tired of it and have blocked their calls.

Many of these calls simply want a live person to answer.  They can then sell numbers to others for profit.  They do not need to sell anything to you.  Only need for you to answer the phone. Do not pick up.

telemarketer asking us to participate in surveys - automated call -

I too recieved the dead air, followed by a hangup.

I called the number back (1-202-803-8929) and recieved a message saying, "Thank you for calling back. If you no longer wish to be contacted regarding special promotions, please press "1" to be removed from our calling list."
The message then said, "Please allow up to 72 hours to be removed from our calling list"

Since they already had my number, figured it certainly can't hurt.
We'll see if they call back beyond 72 hours. ;)

picked up before it went to answering machine,  nothing on the other end but dead silence.  Hate calls like this feel like stalking

Thanks for the update. I have received three calls from that number: 2 calls yesterday, 1 call today. I didn't answer any of them, so thanks for posting. :)

Number called back less than 1/2 hour later.  I answered it this time.  It's a company called "GMI" doing marketing research.  How annoying!!  I thought I was on some government "Do Not Call" list!?!?

Got a call from this number.  Did not answer, no message left.  Who is this??