We are working on auto (license plate as id) based messaging mobile app and searched for if any successful app exists before. What we have found so far:
1-) www.bum.com : last news from 2011 seems to failed.
2-)https://play.google.com/store/apps/details?id=com.marzki.reparkapp seems to be inactive.
3-) http://platewave.com/ focus on dating and UK only and only web and mobile app.