First things first... put your number on the don't call list.
Next thing... when you get the call, ask for the company they work for and their location. Then tell them to put you on their don't call list, and if they call you again, you will contact your state's attorney general to register a complaint against them. Some company recently paid something like US$100 million in penalties for not following the don't call list.
Explain to them that they're calling you on a mobile phone, which is a violation of federal laws. Ask for their contact information so you can pass it along to the attorney general.
If that doesn't work, you can have fun with them. Ask if your bankruptcy would prevent them from providing you credit on the purchase. If they ask what kind of bankruptcy, tell 'em you've read the whole book -- chapter seven, chapter 11, chapter 13...
Ask if they can provide it to you while you're in prison, 'cause while you weren't guilty of that manslaughter charge, they're keeping you locked up until the trial.
Whatever they're offering, tell 'em you've got one that's better. Mortgage? I've got a 1% rate... top that. "Performance" enhancers? Your brother in law is a drug rep, and he gives you all his extra samples.
There's also the police whistle next to the phone...
You could also tell 'em you're the janitor and can't make those decisions. Or you just stole the phone, and you've got to split before the cops come.