Adaffix started their caller ID service in Austria but have now expanded it to the US after rollouts in Germany, Denmark, Sweden, and Belgium. The app is not true caller ID but it does supplement your address book content with real time information from multiple sources. For example, when you get a call the Adaffix app will lookup the calling number over your 3G connection using Yellowbook to tells you the callers name. You can then also add this information to your address book.
They also have the ability to tie your account to your Facebook profile allowing the app to show you up to date status and pictures of your Facebook friends when they call. The other feature in the app is Auto Suggest which will recommend other numbers for companies or services when you get a busy signal. For example, you might try calling a taxi and it would give you an alternate number for that taxi or even a different taxi service number.