I'd pay good money for a telephone that rings differently when the phone number and/or caller's name doesn't come over the Caller ID, especially if the audible ring could be totally disabled for "No Information Available" calls. I'd pay even more money if the phone could remember numbers and/or names that you never wanted to hear the ring from.
Few things induce weekend grumpiness like being woken up early on a weekend morning because the Police Athletic League wants me to give them money. (Sure, I could turn off the ringers before I go to bed, but what if an actual important call needed to get through?)