Any idea?

called my cell #. hung up, didn't leave a message

Called my cell and hung up when I answered.

called them back, its an automated rebate service activated by visiting an affilate website.  you can end the calls by pressing 2 in their menu.

NO.  It is NOT "activated by visiting an affilated website" because I DO NOT use my phone to 'visit websites' and I do NOT give out the number to ANYONE except family, VERY close friends and the occasional doctor.   I CERTAINLY do not 'enter' it into websites so that I can be SPAMMED.   THIS IS unwanted, unsolicited SPAM, and therefore ILLEGAL.

Called my on my pre-paid phone on 5/3/14, but, fortunately, I was doing yard work, so didn't hear it and didn't see it until the next day.  I will BLOCK it, so they cannot bother me again.