Call the number and hope you get voicemail. Leave a panic message obviously being left for someone else (for instance, say that your Jeff's boss and that Jeff had an accident at work and that they need to call back immediately). I get these messages all the time that were obviously dialed wrong. If they are human in any way at all, they'll call you back to let you know that you dialed the wrong number.
When they do, you'll have their name on caller id.
If you don't get voicemail, tell them that you got their number off a restroom stall wall and are inquiring about the free blowjob. You may even get a free blowjob out of the deal.
If it's a guy? I'd pay to hear them call you back and hunt you down.