The CallBlocker answers the phone before you even hear it ringing, running interference for you and putting those telemarketing weasels on notice. You can record whatever message you'd like into it, but here's the default message:
"You have reached CallBlocker and not an answering machine. All commercial sales calls and fund raising requests are not accepted, place this number on your do not call list. Personal and invited callers press 5 on your touch phone to proceed."
The CallBlocker's creators' hearts are in the right place, because wouldn't anyone want to slam-dunk a telemarketer or two? But who is this really going to stop? Surely it will annoy everyone whom you actually want to talk to. Instead, here in the US you could put your name on the National Do Not Call Registry, or go ahead and spend 50 ($94) on this device that will probably be more of an annoyance than a solution.
Product Page [Callblocker Ltd., via Oh Gizmo]