I think people do that half numeral, half spelled-out thing to prevent 'bots from collecting their telephone number.
Despite what that movie
"2001: A Space Odyssey" might lead the viewer to believe, computer heuristics aren't that great yet--not even in 2010 (
"The Year We Make Contact")!
That having been said, there ARE plenty of weirdos on Craigslist.
P. S. Of course, making two silly Arthur C. Clarke references in the same post doesn't exactly acquit me of weirdness--I guess you could say I did it for the HAL of it!
....sorry
