Even if they can get around the do-not-call listing by adking for your phone number, you can either refuse to give the number, make up a number (tee hee hee 555-GET-AWAY!!!!!) or, if you ask for the caller's supervisor they can put you back on the do not call list.  Keep in mind that if they do call you after you've been put on the list (and there's some time frame involved for how long ago you got on the list, I forget how long) the penalties are substantial, so maybe we can all make money filing claims for violating the do-not-call?!!!

PS.  Back when I was a kid, my Dad used to have us tell them he was dead.  Invariably got an apology and a quick hang-up!