Unlike some other services that offer de-centralized calling (see GrandCentral, Jaxtr, JaJah, and iNumbr), LetsCall.Me preserves the caller's number so you can see it before picking up.
Users who want to use the service as a virtual business card can simply make various bits of their contact information publicly available, although the phone number will always remains hidden. In future versions, I'd like to be able to display a wider array of profile information, as well as have a simpler way to manage multiple URLs with the same account. As it stands, you've got to remember which ones you've set up even though they're on the same account.
It's neat. Check it out.