US -
Formally:
123 - One hundred, twenty-three
1345 - One thousand, three hundred, forty-five
120979 - One hundred twenty thousand, nine hundred seventy-nine
1793089 - One million, seven hundred ninety-three thousand, eighty-nine
Like Claudia, I was taught never to say "and" for numbers, and it mostly stuck.
Informally:
123 - One twenty-three
1345 - Thirteen forty-five or Thirteen hundred forty-five
120979 - A hundred twenty thousand, nine seventy-nine
1793089 - One point eight million :). One million, seven hundred ninety-three thousand, eighty-nine