Your number IS disclosed (Score 1)

First of all, this service does NOT block your number. It shows a missed call (on the intended recipient's caller id) from the number that you dialed the Sly Dial service from, THEN it goes to their voice mail. To prove that this is the intended way that this service is supposed to work by Sly Dial, block your phone number before calling their service (dial *67 then 267-SLY-DIAL). Listen to the recording you get from them. It specifically says that you're blocking your number and that your intended party is to know who is Sly Dialing them. It instructs you to hang up, and then call back without blocking your number. The second point I want to make is... just like anything else, once this service becomes popular and known in the public eye, it won't be such a secret anymore, therefore causing people to think that they didn't get a missed call because they were in a dead spot or something, but that they have been "Sly Dialed." You'll get a call back from the person saying, "hey, did you Sly Dial me the other day???"... lol. But for now, I guess it's good for what it's worth in certain situations.