GrandCentral (by Google) is a similar FREE service, but the number that they generate for you is your permanent number. However, you can link that number to all your existing phones and create custom ring setups. Depending on the caller, GrandCentral will ring my cell phone, my wifeâ€™s cell phone, my office phone, or all my linked phones!
Concerning privacy and security, my favorite feature of GrandCentral is the ability to simply mark a caller as spam (just like an e-mail inbox), and never hear from them again! Telemarketer or ex-boyfriend/girlfriend harassing you? Hit the spam button by their number and kiss them good-bye!
GrandCentral is currently in private beta, but you can go ahead and reserve a number.