Fortunately, I keep my cell phone for emergency use only and don't keep it turned on unless I need to use it (don't have voicemail either).  But if I did use it I would be REALLY upset.  I get upset with those calls on my regular line at home as it is.  I generally try never to be rude to anyone; however, I make an exception for telemarketers.  I have not asked them to call me; therefore, I feel no reason to be polite.  Generally, as soon as they start their spiel and I realize it's a telemarketer, I yell very loudly - TAKE MY NUMBER OFF YOUR LIST AND DON'T CALL ME AGAIN.  Then I slam the receiver down as hard as I can.  I used to be polite, and all they did was keep calling back again and again.  I had to threaten one with a harassment lawsuit in order to get them to stop.  They, of course, didn't know that I didn't have a lawyer and wasn't really going to sue, but at least it worked.  They have gotten me out of the bathtub, down off a ladder, running in from the yard.  I certainly don't feel the need to be polite.  AND my phone number is unlisted, so I am certainly not inviting these calls at all.  Frankly, I think telemarketing should be banned.