No one wants to give their last-minute, late-night, drunk-from-the-open bar Craigslist "date" their real phone number. It's this free-sex market that Hookupdigits hopes to tap: the site generates proxy phone numbers that expire after 7 days, good for calls ten minutes or less in length. Other startups have gone here before: Numbr was a disposable call forwarding service, and Jangl gave both halves of the hookup a unique number. Both have since folded. The failures of its predecessors isn't Hookupdigits biggest problem. Let's start with the photo they use as their lead graphic — of San Francisco Web microcelebrities Chris Messina and Tara Hunt, whose "digitally enabled breakup" was so blogged about that it made it into print.Leave aside having a fairly public former couple as the face of their business. It's not clear how Hookupdigits believes they'll turn a profit. One of the players behind the site contacted me offering me "rev share" if I "really loved it." A rev share of what? The Google AdSense ads overdecorating the site? It's a shame that those who would most benefit from Hookupdigits — Internet sex workers and their clients — are exactly the people Hookupdigits can't overtly market to, maybe for fear of being heavily surveilled by law enforcement. What will shut them down won't be police involvement, but lack of a user base. There are still far more people meeting through online dating sites who want to swap real phone numbers before they share anything else — as a sign of mutual trust. Call it old-fashioned. At least if you share your real cell number, you can text your good time, too.