How about a service that uses a Siri-like voice recognition service to do one very limited context task: Screen your calls against telemarketers?
A lot of telemarketer outfits with trashy setups are already at a disadvantage: Their predictive dialers leave a huge gap of silence at the beginning of an answered call because they don't properly time their dialing with available operators. Such a service could learn the vocal characteristics of your family and friends and would probably do a great job with recognizing cues telemarketers produce unconsciously.
You don't really need something that complex. You can either:
1. Just don't answer any call if it's not in your address book, as I do if I'm not at a computer.
2. Do a Google search for the number, if your doctor, tailor, or dry cleaner doesn't come up, don't answer. Add these to your Address Book for the future.
Usually http://800notes.com/ or similar sites will come up for telemarketers, with many notes. If implementing #2 in software, it would make sense to go the other way, validating that a number probably is a telemarketer, instead of validating that it's something relevant to you (which would be harder).
I always pick up the phone, because I don't want to miss a call from a friend or a family member calling from jail, or a hospital, or a stranger's phone after they got in a wreck.
It's less of a concern now that nearly everyone has cellphones, but I'd rather not risk missing a call like that :/
Except that cell phone numbers tend to tell you where somebody lived 5 years ago, as opposed to where they live now. This makes it quite hard to screen based on an out-of-state area code.
I find that doctors offices often call from an unknown number. This is for privacy reasons: if a psych doctor calls and someone who doesn't know I am seeing one sees the caller ID, they would have violated my privacy. Also as a rule they don't leave voice mail messages beyond "this is Dr. So-and-so please call me back." Because of this I always answer all unknown numbers. If they turn out to be a telemarketer, I tell them they called the director of the FBI and ask them who they work for and how they got my number, then promise them to investigate their company because calling this secure line is a threat to national security.
A lot of telemarketer outfits with trashy setups are already at a disadvantage: Their predictive dialers leave a huge gap of silence at the beginning of an answered call because they don't properly time their dialing with available operators. Such a service could learn the vocal characteristics of your family and friends and would probably do a great job with recognizing cues telemarketers produce unconsciously.