UserX
Don't know if it is available in your area or with your phone company, but PRIVACY MANAGER might do the trick! It's not a gadget...it's a service that you add on to your service package and it only allows calls which display their number on caller ID to get directly through to you. Any other calls are screened by the service and the caller has to either announce their name or number...then you get a call with a computer message informing you that you have a call from XYZ or 123-4567 and you get the option to take the call, deny it or play a pre-recorded message informing the caller that you do not wish to receive further calls from them. It virtually eliminates telemarketers and nuisance callers who don't want to give out their ID. A lot of those calls are probably telemarketers...they're relentless!