Is there an application for iphone to block callers from calling me from a blocked number?
Here are a few applications that you may want to look at and see if any of these may work for you.
MCleaner:http://www.mcleaner.com/ , iBlacklist:http://www.iblacklist.com.br/iblacklist/index.php and http://www.trapcall.com/.
I hope this was helpful.
Sprint has tips and resources to help keep them safe and focused.