How long would it take your computer to precompute SHA256 of all North American phone numbers?
Be smart about "NPA" or area codes (there are only about 300 in use). Be smart about the NXX as well. Not all strings 000 to 999 are allowed.
Answer if we are printing to Terminal.app on my MacBook Pro, 2.7 GHz Intel Core i7, Early 2011:
3947385 items complete
108.02 sec
36541.68 per sec
316 npa * 792 nxx * 10000 =
2502720000 items to complete
19.02 hours
Answer if not printing:
7034763 items complete
23.36 sec
301184.66 per sec
316 npa * 792 nxx * 10000 =
2502720000 items to complete
2.31 hours