0121 sounds natural as 'oh one two one'... 'zero one two one' just sounds retarded, and American, which makes it more retarded.
And yet, it's basically universal in America to use 'oh' for 'zero', especially in telephone numbers:
5088675309 => "five-oh-eight eight-six-seven five-three oh-nine" (combining two or three digit blocks into a single number pretty much only occurs for business marketing purposes... e.g one-eight-hundred fifty-four giant, which I suspect the other New England VTers will recognize)
NANP, of course, is the cause for the 3-3-4 breakdown of phone numbers given above: a three digit area code (often enclosed in parentheses) plus a seven digit phone number, of which the first three digits represents the exchange.
Dammit man, we all know Hawaii Zero Zero Zero Zero Zero. Give us some credit!
* actually I know it was 'Five O', but am not really sure why, so it's all a big guess.