It's a legit non-profit (Crohn's & Colitis Foundation of America), with a legit-sounding automated number-removal opportunity that can be accessed by calling back.

After receiving 4 no-ID, no-message calls on 4 consecutive days in August 2012, and another just today, I reviewed the complaint logs on this and similar sites and noted that the calls were all in August and September, and all have the same features (no message, successive calls stopping as suddenly as they started).  Curious and feeling I had nothing to lose, I did something  I wouldn't normally do or recommend, and called the number back.

I received calls from this number on 9/2/11, 9/8/11, 9/12/11, 9/13/11 and 2 on 9/14/11. Then not again until 9/12/12. Dead air if you pick up.

Called 9/12/12 at 12:20 PM EDT. One ring, then stopped.

Caller ID name is Toll Free Call.  Another telemarketer.  No message.

I've received six calls from this number since 9/2/11.With one exception, the calls have come in between 2:24PM and 3:09 PM. One call was at 8:53 AM. We haven't answered any of them.

I've blocked the number.

Have received numerous calls from this number including one yesterday and one today.  I answered once and was disconnected.

Received two calls from this number, one on 9/2/11 and again on 9/8/11. Didn't answer either and no message was left.

Called and my answering machine picked up.  They did not leave a message.

Received a phone call from this number. No message left.

Net 10

Numorus calls from this number with no response when answered.