Without Skydeck, your cell phone can only tell you who is calling you if their number is already in your contacts.
Skydeck Caller ID tells you who is calling you when their number is not in your address book. Let the call ring out and Skydeck will look up the number in multiple databases, and verify the results against the address books of other members who have opted in to this feature. If Skydeck finds a name, it will offer to add the caller to your contacts with one click.