Given what the HNers know about proxies and VoIP, I don't imagine there is a technical solution short of phone networks only accepting VoIP from some kind of certificate authority, which can be aggressively policed (by Western phone companies, somehow motivated to protect their customers and their good name)?
Why is it possible for some creep to call me from ostentatiously fake numbers like "1111111111" or "111 222 333" at 3am only to spout gibberish, try to scam me, or just stay silent on the other end?
Honestly, I'm astonished people put up with this kind of thing. If I was getting the kind of phone spam people are reporting, and no phone company was offering whitelisting, I'd just keep my phone turned off unless I needed it to make an outgoing call.
A bigger problem, though, is that I'd like to accept some calls from strange numbers, like couriers trying to deliver something, or emergency calls from loved ones, or customer service reps calling me back about something.
For whitelisting to be effective, we'd have to change other things about the way the phone network and its participants work.
BTW if all your friends also turned their phones off except when they wanted to call someone, you'd seldom be able to reach them, unless you happened to call just before/after they had made a call.
I realize landline phones are on the way out, but whoever makes a cordless multi-handset phone station with lots of number memory (I've nearly filled my 100 number memory) and features like VIP-callers-only, full disabling of ringer, and maybe even a downloadable spam/charity-call database, they'll get my next phone upgrade.