Alternate communications systems and data sets

I have come up with several ideas for communications services for communicating with people you don't know, drivers and anything you can name. A unifying feature of these, although to a lesser extent the "anything you can name" idea, is the dataset of communications recipients. For drivers the data set is well established: license plates numbers. There are also well established data sets for communicating with people you don't know: zip codes, street addresses, lists of companies, lists of charities, etc. The key to expanding this idea is identifying data sets and getting access to them.