Why do phone numbers never start with '123'?

Answer 1

In some countries, particularly Hungary and Mexico, there are telephone numbers that start with 123.

In older telephone technologies, dialing or touch-toning a "1" first told the system you were about to dial a long distance call. In the phone system circa 1965 and before, there were three kinds of domestic calls: 7-digit local calls, 1+7digit zoned called zoned calls (which called in roughly the same county, but cost more than local), and 1+10 digit calls which were 1 plus a 3-digit area code please a 7-digit number. This rigid formatting worked because voice and routing signals went over the same circuit (so you'd occasionally hear fast tones in call that required longer routing). Nowadays, in most areas, zoned calls are obsolete and area code plus 7-digit numbers are recognized by the system as long distance calls. Even today, however, typing in a 1 first will still notify the system to expect 10 more digits. Note too that we are starting to see area codes that begin with the number "1", and there is a move in the field to go to all 10-digit phone numbers (3-digit area code + 7-digit phone number), so you may see numbers that start with "1" in the not too distant future.