I beleive Ooma can fix all of these by using an anti-spam technique of rejecting everything that isn't whitelisted, and requiring manually approving whitelist requests.
All Ooma would need to do is send all non-whitelisted phone numbers to a time-limited voicemail that says something like "All unknown callers require verification. At the tone, please state your name and the Ooma customer will consider your request"
Then leave about 5 seconds for a recording, which is just enough to say "John Smith" or "Hi, mom, it's me!" but not enough for a harassing telemarketer or bill collector call. I would also limit it to one or two requests from a single number, so persistant callers can't leave a nasty message 5 seconds at a time.
The queue can be shown on the user's "My Ooma" page with a "play button" and a "whitelist/blacklist/send to voicemail" button next to each message.
Premier Service (I was not expecting to do this, but I love the Premier features)
Panasonic KX-TG4024 (w/ 4 handsets)
Customer since November 2010
Internet access: FiOS 15/5
EVERY smart person out here has this idea. COME ON OOMA!! WTF is taking so long to implement such a simple, but needed, feature in today's telecommunications VoIP?!? Get off your lazy asses and give us this, and you'll be the best phone company ever.
Don't do it, and watch as we all flock to Asterisk so we can implement our own INTELLIGENT phone screening. :-/