As for mobile phone numbers being randomly placed inside larger space of all phone numbers, while this makes some sense for US/NANP, in most of the rest of the

As for mobile phone numbers being randomly placed inside larger space of all phone numbers, while this makes some sense for US/NANP, in most of the rest of the world mobile numbers have some semi-well defined prefixes (as in "number that starts with 6 or 7 is certainly mobile phone, discerning what operator is sligthly non-trivial") and even for NANP there probably is some publicly available database that says whether given number is mobile or not.