I have list of all US phone numbers: 000-000-0000 000-000-0001 ...
Yes, this is strange on all fronts. As far as I know names and land numbers are still published in phone books, and a phone number isn't generally a very interesting bit of information to have. And to the extent this information is sensitive, why be so eager to spread it (beyond being a teenager and getting a thrill)?
2. Cell numbers aren't published in those books, which this affects.
2. Land lines these days are somewhat separate from our lives. It's relatively easy to ignore. Getting phishing texts (say, faking our banks, since some -- including myself -- have some bank alerts texted to us) to our cellphones could be quite harmful. If you send a million texts pretending to be Chase, and say 50% of the numbers are legit cell phone numbers, and 20% of people have chase accounts, and 0.1% of people fall for the phishing attempt, then you get 1/10,000 people getting phished. That's 100 people out of a million affected monetarily, and 500,000 people getting annoyed by the spam.
Obviously this is back of the envelope, but this is one reason it could matter.
edit: a comment thread below mentions that the bottom two digits are hidden at this moment but will be revealed for interested parties. That really smells like the numbers will be sold to spam/phishing operations.