From what I've heard, it's against the law for Telemarketers to call cell phone numbers. And if you tell them it's your cell phone, they will usually say I'm sorry and hang up. There is a web site you can go to get on that do not call list but I forgot what it is called.
Anyway, smurf they were right about ignoring people. And you can also laugh along with them. The main thing is to let them know it doens't bother you.
It's like if I do something stupid like nearly fall over my own feet, I'll just make a little joke about it and carry on. Which is different, but I'm trying to make a point...