I would guess the catch is that you voluntarily type in 10 phone numbers. See if there's any fine print concerning what can be done with those phone numbers by the site.
This is the first pornsite I've found in years that I'd actually advertise to swarmers. When you first load it up, it looks just like every crappy scam site out there, except that it's real. It's huge, it's updated constantly, there's no spam, no popups, and no bullshit -- and it's completely free. When you sign up through that link above and respond to the confirmation email, I make a bit of loose change.
See what other swarmers have to say about it. People love this place, so I feel fine about sending you there and am confident you will enjoy boners.
